An apparatus and method for canceling narrow-band interference in a wideband mobile communication system. The apparatus includes a down converter for down converting a received signal into a baseband signal, an analog-to-digital converter for converting the baseband signal into a digital signal, a decimation filter for decimating the digital signal according to a decimation ratio, an interference canceller for detecting narrow-band interference signals contained in an output of the decimation filter, and canceling the narrow-band interference signals, and a demodulator for demodulating an output of the interference canceller.