Maybe,that's why scientists all over the world are still researching on it.
There is a vast universe in front of us so obviously there's no doubt about it that we're not the only mentally capable creatures that exist here.. there can be a millions of planets with a chance of existence of life.
Even with the recent scientific development of most solar systems being composed of irrelevant and uninhabitable ghost planets, there is undoubtedly billions of planets (if not more) that can sustain a complex species, possibly, longer than earth has in our universe. The question isn't 'are there aliens?' it is more appropriate to ask if intelligent life has visited earth!
The universe is huge!
Its pretty silly to say we a speck of dust in the vast universe is the only place that has life. Now intelligent life that would be more rare.
I think the most likely form of alien life would be single celled organisms and bacteria. So yes I do think there are aliens