A protection circuit for a central processing unit (CPU) includes a power circuit, two comparators, a number of resistors, a thermistor, and an electronic switch. A non-inverting input terminal of the comparator is coupled to a first power terminal. An inverting input terminal of the comparator is connected to ground through the thermistor. An output terminal of the comparator is coupled to the electronic switch. When an operation temperature of the CPU exceeds a predefined temperature, the comparator enables the electronic switch to be turned on, to reduce an operation frequency of the CPU.