  The frequency dependent transport is investigated for a two-dimensional
disordered system under QHE conditions. The real and imaginary parts of the
conductivity are calculated numerically in linear response using a recursive
Green function technique. The energy dependence of $\sigma_{xx}(E,\omega)$ is
obtained within the lowest Landau band. When the width of the system exceeds
the characteristic length, $L_{\omega}=(\hbar\omega \rho(E))^{-1/2}$, the
maximum of the real part of $\sigma_{xx}(E,\omega)$ decays with frequency
almost linearly which is different from the classical Drude behaviour.
