An electronic system includes a fan module, an embedded controller, a reference microphone, an error microphone, an active noise cancellation controller, and a micro speaker module. The reference microphone is configured to output a wide-band noise signal associated with the operation of the fan module. The error microphone is configured to output an error signal by detecting the noise level during the operation of the electronic system. According to the wide-band noise signal, the error signal and the fan information provided by the embedded controller, the active noise cancellation controller calculates the narrow-band noises and the wide-band noises generated by the fan module, and drives the micro speaker module accordingly for providing a noise cancellation signal. The error signal may be reduced to zero by adaptively adjusting the noise cancellation signal for canceling the noises generated during the operation of the electronic system.