Fan keeps running after the engine is turned off

You don't say what kind of car it is, but a lot of cars have temp sensing engine fans that will continue running after the engine is turned off. This is the reason the engine isn't overheating. It may also come on if it's really hot and you are in heavy traffic with the A/C on. Also, it may come on after the engine has BEEN off. The computer will sense what needs to happen. Not knowing the car, and with the info I have, I'd say you have nothing to worry about.

Nothing to worry about ,, a lot of my cars do it also , just heating sensor's ,, its good for the car

Yea, means your car might be low on radiator fluid. I'd start there first.