In a CDMA mobile terminal, the power supply voltage of the mobile terminal is compared with a first threshold voltage, and frequency monitor is performed at a normal rate if the power supply voltage is higher than the first threshold voltage, and frequency monitor is performed at 1/N of the normal rate if the power supply voltage is lower than the first threshold voltage, where N is equal to or greater than 2. Additionally, the power level of an RF signal received by the mobile terminal is compared with a first reference level, and frequency monitor is performed at the normal rate if the power level of the RF signal is lower than the first reference level, and frequency monitor is performed at 1/N of the normal rate if the power level of the RF signal is higher than the first reference level.