It's officially spooky season at Myles Garrett's house ... 'cause the Cleveland Browns superstar has decorated his home for Halloween -- with gravestones of NFL QBs!!!

The 25-year-old put out the set up at his Ohio pad just a few days ago ... laying headstones on his front lawn with seven quarterbacks' last names, numbers and helmets on them.

The list of signal-callers features opposing players on the Browns' schedule this season ... including AFC North rivals Lamar Jackson, Ben Roethlisberger and Joe Burrow.