A receptacle that is hot with nothing plugged in is a sign of wiring failure. This may cause a fire at any time. PLEASE turn off the circuit breaker to this receptacle immediately and call a qualified electrician to correct the problem. Do not do this yourself, even if you have some qualifications, there are major problems you will likely miss.
99.9% of the time this is just going to be a loose connection at the receptacle. I bet you are also =having problems down stream (flickering lights etc). An AM radio is probably painful to listen to. Mr Brown is right. Get this checked out before you have worse problems.