"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?