gas pedal goes down and car surges ahead while driving

I had just filled up and was going to park in a parking space. I made the turn to pull into the parking space when the accelerator went down and my car surged ahead. I could feel the gas pedal go down under my foot. This has also happended on the open road, riding down the road and the gas pedal goes down on its own and the car surges ahead. I throw my brakes on and all is well, then it does not happen for quite sometime. I purchased the vehicle new and it has happened about 5 times since purchase.