If and when an oven is coming on or doing anything by itself, this is very dangerous and can result in a fire.
So until it is repaired, please leave it unplugged or leave the door open when it's not in use, and of course one should never
leave a microwave unattended while cooking.
Chances are you have a shorting membrane keypad.
Please let me
know your full model number and more details on what it's doing and I can give you the information you need.