What does this mean??

I had a situation recently and I'm curious what other people think it might mean.

A guy keeps staring at me without smiling. There wasn't any smiling or flirting. He talks nicely to other girls he not shy kinda. But I'm not sure. Last time i stared back and he was looking serious like he was analyzing me or face read kinda stuff I think he thinks tht I like him . What to do??

What do you think this kind of behavior usually means? Was he interested, just curious, nervous, or am I reading too much into it?