A method of operating an application processor including a central processing unit (CPU) with at least one core and a memory interface includes measuring, during a first period, a core active cycle of a period in which the at least one core performs an operation to execute instructions and a core idle cycle of a period in which the at least one core is in an idle state, generating information about a memory access stall cycle of a period in which the at least one core accesses the memory interface in the core active cycle, correcting the core active cycle using the information about the memory access stall cycle to calculate a load on the at least one core using the corrected core active cycle, and performing a DVFS operation on the at least one core using the calculated load on the at least one core.