"Misbehaving" means doing something that you're not supposed to do.
You usually use "misbehave" when talking about children:
He's been misbehaving in class.
The noun form of "misbehave" is "misbehavior":
This kind of misbehavior will not be tolerated!
Occasionally we use "misbehave" to talk about adults. In those cases, it has a kind of sexual tone.
A: Have you been misbehaving?
B: Oh yes. I've been very bad. Are you going to punish me?