How to react to him staring at me?

this guy who is in one of my classes at school, spends practically the whole of every lesson staring at me, when he sees look back at him, he always smiles at me. we've never really had a proper conversation but i have spoken to him and joked with him a couple of times. i just don't know what to do when i catch him staring at me. i'm worried that if i just turn away shyly he will think that i don't like him back?