A type of mental problem?!

A type of mental problem?

Ever since I was like 9 I began talking to myself. I sometimes pretended to "act" out. Its kind of hard to explain but here it goes: Right after seeing a movie I would like I would picture myself in that movie and I would do as if I was carrying out a conversation with someone I made up or someone in the movie. After I finish talking I change my voice and talk back.
It gets even weirder I can control it. Like I won't do it in public. Its only when I am alone. I tried telling my best friend but she took as a joke and said eveyone talks to themselves. I neverminded it until now. I rather live in this make believe world than talk to my friends or study for school.

I want to know if this is kind of normal or if its a serious issue.

I'm no shrink, but it seems to me that if you are aware of the behavior, and you can in fact control it, it is not a serious problem. It sounds like you use this as a technique to deal with your fantasy life. If you are able to function in the 'real' world. ie; go to school or go to work. No worries. You say that you have friends, therefore you can function in society. Bottom line; as long you can keep your fantasy life separate from the rest of your life, you are healthy.