Maybe there's a booger in your nose. Really though he more than likely likes you. Most people are afraid of rejection so they don't act on how they feel, so if you don't mind him staring at you just go say hi.
It depends on how he was staring at you, the look he had on his face and how long he stared at you and how it made you feel. If he stared at you for just a little bit and then looked away, he probably likes you. If he stared at you a long time without ever looking away, you may have a problem with this guy. But the bottom line is, how it made you feel and go from there. Always go on your gut level feeling. Good luck! : D