If you answer "yes" to most of these questions then he probably does, ask him! If you answer "no" to most of the questions, he probably needs to get to know you better. Ask him to bring some of his friends to join you and your friends on some activity; movies, sporting events and playing games are all great ways to start getting to know someone. They keep away awkward moments and pretty much guarantee a good time, regardless of your age.
If you are about 18 or older:
Does he talk to you?
Does he smile at you?
Does he go out of his way to spend time with you?
Has he complimented you?
Has he given you a gift?
Has he asked you to hang out?
Does he walk close to you?
Does he listen when you talk?
Does he look you in the eyes?
Does he find a reason to brush against you?
Does he ask you for your opinion?
If you're in high school or grade school, as above but can also include:
Does he tease you?
Does he stop his friends from teasing you?
Does he act "strange" or differently around you then around his friends?
Does he look at his shoes, the wall, empty space, anywhere but at you when talking to you?
Does he fidget around you?
Has he asked for your help with homework?
Does he laugh at your jokes, maybe a little too loudly?
Does he try to gross you out?
Does he pay more attention to you in gym class then to other kids?
In the end, the best way to find out is to ask him. Wait until he's away from his friends, but not in a rush to be somewhere. That way neither of you will feel terribly embarrassed about being so forward.