Is it okay if im a Christian and believe in aliens and dinosaurs?

Dinosaurs were actually called dragons for years, and the term dragons is in the Scriptures, and the description of a Behemoth and a Leviathan are of a land dinosaur and a sea dinosaur. As far as aliens go...no, they do not exist — the fallen angels do exist however, and they can speak to people. 

The Bible gives us warnings not to believe every spirit (every angel). Fallen angels will not look like red guys with horns and pitchforks... they are angels. The holy angels of God will never tell you anything which is contrary to God’s words. The Bible warns that any angel who gives another gospel, which is different from the gospel, is not a HOLY angel of God, it is an angel which is in rebellion against Him. 

People need to be so careful about being wooed over the supernatural, of miracles, and power - because all of the angels have power - the good and the bad. In the end times, the false prophet will perform signs, miracles, and wonders such as calling fire down from the sky, and after receiving a deadly head wound (note: his right eye utterly darkened) - he will be resurrected from the dead. The Bible gives to us these warnings in order to protect us, and read Deuteronomy chapter 13, as it bears some relevance here as well. 

Well, I'm a Christian and understand that dinosaurs existed for many millions of years ...

so, maybe you don't know that not all Christians hold a "young-earth" view.

Or maybe you are just framing the question as such to create a straw-man.

IMO, one cannot get the age of the earth (or universe) out of the Bible unless they make a number of assumptions to come to a per-determined interpretation.

(As Bishop James Ussher did in the mid 1600s)

As far as aliens go:

I see no reason to think aliens exist ... from what I know from science.

Yes, you can believe in those things and certain other things not incompatible with Catholic teaching.

why?  do you believe in that myth about hell or something?  go call an exorcist if you're THAT concerned!

Christians believe in scripture. According to scripture:

1) 'Ghosts' are demons called 'familiar spirits' which are the lowest level demons that are assigned to families and lineages. They can take on the visages of departed family members and are experts of those families, personal relationships, even individual personal mannerisms, memories, etc...

However, after death human souls immediately either enter 'Hades' and remain deeply unconscious awaiting judgment, or into 'heaven' where they continue to learn and develop. They do not actually appear to the living as individuals. Anyone experiencing this phenomenon is being deceived by a low level demon.

2) 'Demons' are higher intelligences which are completely morally depraved and which have arranged themselves into a hierarchy of authority, influencing everything from individual families to geopolitical forces using mostly unwitting human 'surrogates' and have righteous counterparts called 'angels' who do similarly. 

Both have been described across all human cultures as inspiring specific arts and sciences, social movements, religious systems and even founding entire nations, some exacting a predictable price in human blood and treasure for their knowledge, (i.e. 'demons'), while the others offer genius and gifts freely within the ordinances of GOD, (i.e. 'angels').

3) 'Aliens' are also demons sentenced to what the Bible calls the 'untraversable abyss of outer darkness,' (i.e. 'space'), where they are being imprisoned inside 'pits of blackest darkness reserved for judgment,' (which sound a lot like 'black holes'). They cannot travel to earth, though they can apparently influence people here through fellow demons still present here, (those not yet sentenced). There is no other 'life' in the abyss of space, which is actually GOD's 'factory seconds' representing every possible inferior version of His two masterworks, 'heaven' (currently inapproachable), and 'earth';

4) 'Dinosaurs' are remnants of the previous 'age' which actually does not share a common 'chronology' with this age. An 'age,' (Biblical Greek: 'aion'), is actually an event  flow with a very specific beginning and ending, but it is not part of one simplistic unbroken chronology as modern man assumes. 

At the end of each 'age' GOD resets everything and often even changes the fundamental 'laws' of reality. However, GOD sometimes allows certain elements of Creation to survive intact from age to age, giving us the impression that there is only one chronological history linking them all together and requiring an explanation. 

Attempting to do this is why the scientific accounts require profound absurdities, incredibly vast spaces of time and other 'miracles' to occur, like life overcoming one in one duodecellion odds to spontaneously form on its own and evolve into intelligent life without being 'seeded' or 'guided.'  There is no actual connection between 'ages.' The ONLY commonality between all ages is GOD Himself their Creator.

The bible speaks of dinosaurs in Job 40 and Job 41. The behemoth, as described in Job 40:15-24 has a large tail and strong bones, among other descriptions that don’t appear to point to any known land animal we’re aware of on earth today,

Aliens are probably some type of demonic spirit.......Ephesians 2:2

the spiritual forces of evil in the heavenly realms” Ephesians 6:12

There are no "aliens".  If there were, the Lord would have warned us to beware of them.  They don't exist.  There are devils and people that want to deceive you into thinking there are "aliens" for other destructive goals.  So forget all that.  Here is what you need to believe:  The Lord Jesus Christ is God, and He loves you.  Believing in the Lord Jesus Christ means being forgiven all sins past and future, and means going to heaven and not hell.  Death leads to immediate heaven or hell, and it is too late to be saved, after death.  All believers still sin.  See 1 John 1:8.  To be in heaven and not hell, believe in the Lord Jesus Christ, who is God and who died on the cross and shed His blood to pay for all of our sins in full, and who was buried, and who resurrected from the dead.  The only way to avoid hell is by believing in the Lord Jesus Christ, without adding any of your own works.  See Romans 4:5, 1 Corinthians 15:3-4, and John 3:16.

Yes, of course.  God has placed his children on countless worlds, and those fossil creatures really did exist.  God isn't going to lie to us by planting fake fossils, and Satan has no creative power.

Sure you can.  You simply mean that you believe that space aliens exists - but in my opinion it is more logical to say you don't know whether they exist. Christianity has no doctrine about space aliens, one way or the other.  

It has no doctrine on dinosaurs either.  Some religious groups may deny the existence of dinosaurs, but Christianity as a whole is not concerned with this.  

Similarly, Christianity has no position as to whether there is a purple house on my street.

Choose one or the other clown