  Anisotropic disordered system are studied in this work within the random
barrier model. In such systems the transition probabilities in different
directions have different probability density functions. The
frequency-dependent conductivity at low temperatures is obtained using an
effective medium approximation. It is shown that the isotropic universal
ac-conduction law, $\sigma \ln \sigma=u$, is recovered if properly scaled
conductivity ($\sigma$) and frequency ($u$) variables are used.
