I would try removing the key from the ignition and closing the door a several times and (HAVE KEYS IN YOU HAND) see if the problem continues. If it does, there is a problem with you locking system or you have a new feature that nobody else has.
If it doesn't something in you purse must have hit the lock button on the remote.
I never lock my X when it's parked in my garage.
02 MDX/NAV/Touring, Blk/Saddle, Towing Package, Cargo Cover, Net and Seperation Net, BSM, Rear Splash Guards, Weather Tech Mats & Cargo Tray, Wheel Locks, Form Fit Deflector, Manik Side Steps, Extended Warranty.