Why does he look at me with no expression on his face?

I've been seeing this guy around town a lot and he always looks at me (not ALWAYS like in a creepy way, but enough to get me thinking) without a smile and when I turn my head to look at him too (he's really cute!), he turns away real quick. He does this to me a couple of times a day. Is he interested or creeped out (because I catch him looking at me so therefore he thinks I look at him a lot too which isn't true - I only look at him sometimes)? And what's with the no expression thing?