A frequency calibration method for a programmable oscillator includes the steps of: counting an oversampling number of an oversampling signal and estimating an accumulated bit number of a USB data stream according to the oversampling signal; calculating a difference between the oversampling number and M times of the accumulated bit number when the accumulated bit number is larger than or equal to a predetermined value; and determining a frequency calibration step of the oversampling signal according to the difference. The present invention further provides a frequency calibration device for a programmable oscillator.