Keyshawn Johnson -- I'm NOT Moving Because of Justin Bieber

Keyshawn Johnson is saying sayonara to his Calabasas mansion -- but the ex-NFL star is adamant the move has NOTHING to do with his beef with his pain in the ass neighbor Justin Bieber.

TMZ spoke with a rep for the ESPN star who tells us, "Keyshawn is not moving to get away from Bieber. He's moving to be closer to the high school where he'll be coaching and where his son will be playing football."

Keyshawn recently took a job as a wide receivers coach at Mission Viejo High School in Orange County, CA ... where his son will go to school in the fall.

FYI -- MSVH is a high school football powerhouse and Key's rep tells us Johnson took the job with the varsity team to "have fun" while his kid pays his dues on the JV squad.

Of course, Key probably won't miss Bieber when he parts ways with his Calabasas palace -- 'cause as everyone knows, Justin has been the neighbor from hell ... partying on the time and speeding up and down the quiet streets in their private gated community.

Key's 11,746 square foot home is currently on the market for $8.5 mil. We're told Johnson plans to move to another mansion near the high school ... but he's very interested in coming back to the Calabasas area in a few years ... 'cause he likes it out there.