Conductive fibers, when added to cement-based composites, appear to have a negligible effect on the DC resistance, but play a dominant role in the intermediate and high frequency AC behavior. The present work, utilizing both physical and computer simulations, has shown that these phenomena arise due to polarization layers (charge transfer resistance/double layers and/or oxide films layers) on the surfaces of conductive fibers. Under DC and low frequency AC excitation, these layers act to insulate the fibers and their effect on transport through the composite is negligible. As frequency is increased, however, the surface layer impedance goes to zero causing the fibers to act as short-circuits in the composite. The result is the subdivision of the single o Nyquist arc, in the case with no fibers, into two separate arcs. Whereas the fiber aspect ratio is a negligible factor in the DC resistance and low frequency AC impedance, it plays a major role at high frequencies. The diameter of the high frequency arc is a combination of bulk paste resistance (between fibers and between fibers and electrodes) and spreading resistance due to current-bunching at the fiber tips. Equivalent circuits were presented to explain both DC and high frequency behavior based upon a frequency-switchable fiber coating model.