AFCI keeps tripping after power outage
If you've disconnected everything from the circuit there are only two causes I can think of - either the breaker is bad, or there is a legitimate arc occurring and the breaker is doing its job and possibly preventing a fire.

If you are comfortable opening your breaker panel, you could try replacing the breaker with a new breaker.  If it still trips, I think that's a pretty definitive sign that there is an arc occurring. At this point, you probably want to call a licensed electrician to come diagnose and solve the issue.  It could be a bad connection or a damaged wire.