CB Mass (Critical Brain Mass) is a now-defunct Korean hip hop group featuring members Choiza, Gaeko and Curbin. Choiza and Gaeko originally met in the sixth grade but before forming CB Mass they began an underground hip hop group named kod along with Sixpoint and Zason, who joined in 1998. In the same year, Choiza and Gaeko met fellow rapper Curbin and created CB Mass.
The group debuted in 2000 under Drunken Tiger's wing and released Massmediah to moderate success. In total they produced three albums: MassMediah (2000), Massmatics (2001, their most commercially successful, with 120,000 copies sold in Korea) and Massappeal (2003). They disbanded later in 2003 after a heated and public dispute where Curbin was accused of stealing money from the group.
After CB Mass broke up, Gaeko and Choiza formed Dynamic Duo while Curbin announced plans to go solo but has not yet released any material.