Having unexpected erections, especially during puberty, is totally normal. They usually happen when a guy thinks about something sexual but they can happen for any other reason too. Unexpected erections can be embarrassing to deal with but keep in mind that you’re not alone. Your friends and others your age are experiencing the same thing. When you feel an unwanted erection coming on try to switch your thoughts to something nonsexual such as your homework, a sports game, or just try to clear your thoughts. Meditation also helps. The good news is random unwanted erections become less frequent as you get older.