The name "Alien" in it self (to me) is naive, the word suggests that the being is foreign. Maybe its just me but as much as I look at things on a small scale, I also analyze them on big and in this case astronomical scales. As much as we all come from the same planet, we all come from the same universe, multiverse, megaverse.
That being said. Yes there are other forms of life out there. 110% the answer is yes. There are billions upon billions of other galaxies out there. more than 100 billion galaxies each containing hundreds of billion stars, each having planetary bodies orbiting them. When humans look for life out there they seem to always look for life similar to themselves (carbon based life) however there could be life based on many different things existing in many different ways. Add string theory into this equation and the possibilities become staggering for life. Taking the multiverse theory into account, there could be life just out of phase with ours, they could be in your living room with you right now and you nor they would ever be able to sense each other.
Earth Humans should also understand that human beings from earth are most likely not natively evolved from their current planet, Earth. When earth humans look for life in the cosmos they look for 3 classifications. Type 1, Type 2 and type 3. In order to keep this post short I will not explain all 3 of these classifications but I will say this. According to earth human classifications; Earth humans are not even on the scale yet. Earth humans are 0.8 on the scale and have yet to reach Type 1. Earth humans are scheduled to reach full type 1 aprox 2080 - 2100 AD (this may vary depending on future historic events)
Back to what I was getting at. It is most likely that Earth Humans have been seeded by a type 3 civilization some time ago, and to be truthful, earth human history mythology, biblical literature, and Earth historic record suggest that is the case. That being said no human on this planet and most other life forms that exist in the cosmos is most likely from their "home planet" Some will be but not all. This also depends on the "seeding" methods of the said type 3 civilization.
Also understand that in cosmic time, the entire human existence would be to that of looking at a microscopic pin sized line in between a millimeter mark on a tape measure, if the tape measure was about a million million times longer than a normal tape measure. Now figure a race from another planet that had just 2 times that span would be 100's of millions of (Earth years) ahead of Earth Humans. Just something to think about.