Provided are a method and apparatus for encoding an audio signal and a method and apparatus for decoding an audio signal, in which errors generated during encoding and decoding of the audio signal are reduced to enhance the audio quality of a reconstructed audio signal. The method of encoding the audio signal includes detecting a pitch of the audio signal, determining a filter coefficient based on the detected pitch, performing second filtering on the audio signal, based on the determined filter coefficient; and encoding an audio signal resulting from the second filtering.