Violent thoughts and mental images?

For as far back as I can remember, I've always had the strangest thoughts. I would be in a room with a bunch of people, and thoughts about how I could kill or horribly injure the people in the room would flash through my mind. Many times this would produce a veritable cornucopia of imagery. I would picture the way that I would do in certain people. Now that I'm older, and still having these thoughts, I've decided to do something about it. I would never actually do the things that I picture in my mind, but it still worries me. Anyone have any idea what might be wrong with me?