Listen to Justin Bieber on iHeartRadio

(TMZ) - Justin Bieber's BFF Lil Za has just been arrested for drug possession at the singer's home -- during an early morning raid stemming from the Bieber egg attack on his neighbor, TMZ reports. 

So far, no word on what type of drugs officials believe Za was carrying at the time of his arrest ... but, according to TMZ, Za was arrested on FELONY drug possession. 

Za is a rapper who once lived at Bieber's Calabasas home ... and he's been tight with JB for years.