Depends, if you want something to come of it or not - if you do, then yes, tell him. I had a crush on a friend and I told him, which a huge thing for me to do. He didn't feel the same way about me, which was horrible, but I did feel better for telling him. We're still great friends, hopefully he feels like that too. If you're happy for it to stay as crush, because crushes can be nice little dreams to make your life a bit more exciting, then no, don't tell him, keep it your little secret and lust after him in private.