Just a guess, but it could be a faulty door latch. Just replaced a microwave in my kitchen because the door would not latch properly when you closed the door. As a result the light and fan would come on. In that situation, the actual oven was "NOT" active, just the light and fan. If you lifted the door as you closed it and held your mouth just right, the light/fan would stay off and all was good. BUT if you bumped the stove or kicked the dog, it would pop on. Was a 9 year old unit so I just replaced it as it wasn't worth $$ to repair.
If under warranty contact Jayco.