heater/air conditioning fan

[lvaj1]

I live in Las Vegas. Commonly this time of year the engine compartment fan will remain on for some time following a drive and parking in garage. Over the past few days, the heater / air conditioning fan has also remained on blowing air out the dash vents. All electrical switches are off and no indicator lights are on. If car is restarted and then turned off again, this has seemed to resolve the problem. Is this a normal cool down feature of some kind ? Or is it the start of an expensive problem.