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 outputs a wide-band noise signal associated with the operation of the fan module. The error microphone outputs an error signal by detecting the noise level 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 provides a speaker control signal by calculating narrow-band and wide-band noises of the fan module, and drives the micro speaker module to provide a noise cancellation signal which is adjusted according to the wind pressure under the current fan speed of the fan module. The error signal may be reduced to zero by adaptively adjusting the noise cancellation signal for canceling the noises in the electronic system.