in a mobile communication system , a method of setting a reverse activity bit is provided . the method comprises measuring a rise over thermal noise - measured representing a load degree of a reverse link ; comparing the rotm with a setup reference value ; setting the rab to lower data rate of a terminal , when the rotm is greater than the rotm_th ; enabling a base station to receive and monitor a variation state of the rotm , when the rotm is less than the rotm_th ; and setting the rab to control the data rate according to the variation state of the rotm .