A method and apparatus for transmitting a happy bit indicating whether a UE needs additional resources for uplink data transmission in a mobile communication system supporting an uplink packet data service are provided. The UE sets a happy bit for a current process based on a different criterion, depending on the current process is an active process activated for scheduled transmission or an inactive process allowed for non-scheduled transmission. A Node B interprets happy bits received for a plurality of processes and interprets them according to the types of the processes. Then the Node B determines an allowed maximum data rate and the number of active processes for the UE and schedules uplink data transmission for the UE according to the determination result.