I second Fimum Fit's opinion. -Bad ignition switch.

I have seen cars turning radios and power antennas on and off whenever they felt like it, due to a worn out switch.

Do you by any chance have a 'heavy' set of keys dangling in the ignition? (lots of keys in your keyring). The weight from this will put a lot of unneccesary stress on the switch.

Freestyler