An apparatus and method for processing an encoded signal are discussed. The method includes: if a coding type of an audio signal is a mixed signal coding type, extracting spectral data and a linear predictive coefficient from the audio signal; generating a residual signal for the linear prediction by performing an inverse frequency conversion on the spectral data; reconstructing the audio signal by performing a linear prediction coding on the linear predictive coefficient and the residual signal; and reconstructing a high frequency region signal using an extension base signal corresponding to a partial region of the reconstructed audio signal and band extension information.