No go in my '95 Buick LaSabre

Three times while driving my Buick I push on the gas and it doesn’t go. It has happened on the highway going 60, after being at a stop light and when pulling into a parking space. The lights and such stay on it just won’t go. I turn it off and back on again, and then it’s fine. The mechanic said there is nothing on the computer and they can’t find anything wrong.