Justin Bieber -- Walking Out with Mayweather?? ... HELL YEAH!!

Floyd Mayweather will have 145 pounds of dynamite by his side when he walks to the ring to fight Manny Pacquiao ... because Justin Bieber says he'll DEFINITELY be in Money's entourage.

Bieber has accompanied Floyd to the ring before -- they've been close friends for years -- but due to the magnitude and importance of this fight, people were wondering if Floyd would go at it alone this time.