A method and apparatus for controlling an active time period during a Discontinuous Reception (DRX) operation in a User Equipment (UE) in a mobile communication system. The method includes transitioning to an active state from a sleep state; extending an active time of the active state, if control data indicating transmission of new user data is received on a control channel; receiving a control signal indicating a termination of the active time; and transitioning to the sleep state from the active state, based on the control signal.