He probably doesn't know unless you have been giving him indicators of interest (IOIs). look them up on google if you want to know exactly.
If you are really acting shy and flustered when you are around him, he may think you have a crush on him or he might think you are just socially awkward. But you say you try not give out any weird body language so theres no reason to speculate.
Im far from an expert on girls (very far) but ive had a few that i know liked me but i was too nervous to ask them out. i knew they liked me because:
1. when i talked to her, her face lit up and smiled at me and she directed her whole body to face me.
2. she laughs at a lot of things i say, even if they are not jokes
3. she kind of talks about herself a lot.
if you do any of these, he knows you like him