A frequency calibration apparatus and method are provided. An oscillator of the frequency calibration apparatus has an operation frequency. The frequency calibration apparatus receives a plurality of time packets from an NTP server at a plurality of first time points. Each of the time packets records a second time point that the NTP server transmits the time packet. The frequency calibration apparatus calculates an offset for each of the time packets in a subset of all the time packets, calculates a clock skew according to the first time points and the offsets of the time packets in the subset, calculates a difference between the clock skew and a standard frequency value, determines that an absolute value of the difference is greater than a threshold, and adjusts the operation frequency to an initial frequency after determining that the absolute value of the difference is greater than the threshold.