2000 neon engine wont turn off

Hi.
I have a 2000 Dodge Neon. This has happened on a few occasions

I puklled into my driveway and turned off the car.. When I exited the car I noticed car was till running. out of curiosity i put the car in reverse and I was moving.. then i put it in drive and sped out of my drive way with the keys in my pocket...

So I called up my sisters boy friend who knows a few things about cars and he says he never heard of it... I asked him how I should turn my car of.. He told me to unhook the wire to the engine.. so i unhooked 3 spark wires and engine cut out.. I then turned the car on and it did the same thing..
any help would be apreciated