1997 Other Oldsmobile Models 6 cyl Two Wheel Drive Automatic

i have a 97 oldsmobile LSS and when i shut my car off the heater display and the heater itself stays on even when i take the keys out. My car usually keeps the radio and heater on when u first turn it off until u open the door it than turns off all of the power it doesnt do that anymore...heater is on all the time...so i am forced to unplug the battery every time i have park it...so i was wondering if i could get a idea of what could be causing this to occur? any help will great thank you