The present invention relates to a method and apparatus for activating carriers in a mobile communication system, and includes determining, when an instruction message for aggregating multiple carriers is received, a bit position per carrier according to an identifier per carrier in the instruction message; checking, when a carrier state message including a state bitmap indicating state per carrier, the state per carrier according to the bit position per carrier in the state bitmap; and activating/deactivating the carriers according to the per-carrier states. According to the present invention, it is possible to minimize signaling overhead caused by carrier activation and deactivation.