Justin Bieber Performing at Takeoff's Memorial

Justin Bieber is performing at Takeoff's memorial service this week ... TMZ has learned.

Sources familiar with the situation tell us JB is set to hit the stage Friday at the State Farm Arena in Atlanta. Unclear how long his set will be or what exactly he might be performing ... but we do know he'll be there and mic'd up to sing.

Justin doesn't have any solo songs with Takeoff specifically, but he's done a couple collabs with the Migos -- "What You See" and "Looking for You" -- plus another couple with Quavo ... so there's a connection there.

Bieber doesn't appear to have posted any tributes to Takeoff, but this might be the ultimate way to honor the late rapper. Bieber's and any other performance is gonna be a closely guarded secret the day of ... all phones are going to be confiscated from anyone attending.

Worth noting ... Bieber postponed his world tour earlier this year to focus on his mental health, so him coming back to this is significant.