A/C compressor is not turning off

Do you have defrost selected? If so the A/C will run to dry out the incoming air to help prevent the windshield from fogging.
I you do not have defrost on, it is possible the clutch has an issue and is causing the compressor to keep turning. With the engine off, you can move the tension-er and loosen the belt. Now try turning the drive pulley by hand to see if the clutch is damaged.

Remove the A/C relay from the under hood relay box and see if it shuts off. If it does then swap the relay with another one in the box and see if the clutch re-engages. If it stays off the relay you removed is bad.
If it turns back on you will need to use a scan tool to test the PCM and determine if it is commanding the compressor on and why. It may be a faulty PCM or control head. For both you need a good scan tool to test the system.