by characters typing by themselves do you mean that if you are on a screen the keyboard just types like thisssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss and keeps on repeating the same key?
if so, likely you have a stuck key.
if that is not what you meant, please specify "what is typed" and "when" as well as "what you were doing at the time" on the keyboard.