An apparatus for generating an in-phase/quadrature-phase (I/Q) signal in a wireless transceiver is disclosed, including a local oscillator for generating an oscillation signal, and first and second mixers for mixing an oscillation signal with a transmission/reception signal to convert the transmission/reception signal into a baseband or high-frequency signal. The apparatus includes a phase locked circuit for controlling the local oscillator, and a polyphase filter installed between the local oscillator and the mixers, for separating the oscillation signal from the local oscillator into an I signal and a Q signal depending on a control signal from the phase locked circuit, and outputting the separated I and Q signals to the first and second mixers, respectively.