CPU scheduling is considered as the basic job within the operating system. Scheduling criteria including waiting time, context switches and others have been suggested for comparing CPU scheduling algorithms. In this paper, a modified version of Round Robin algorithm is introduced as an attempt to combine the advantageous of low scheduling overhead of Round Robin and favor short process to minimize the average waiting time and number of context switches of running processes in interactive (time-shared) systems. A threshold is considered to determine whether the running process will be interrupted because of the expiration of its time slice specified by the Round Robin policy or will continue execution until termination. Derived results show that the suggested modification minimizes the average waiting time and number of context switches compared with Round Robin algorithm.