The electrical response of carbon fiber reinforced cement mortar over the frequency range 1 Hz-10MHz has been presented. The low frequency conductivity is shown to be directly influenced by increasing fiber dosage, with conductivity percolation occurring at dosages in the range 0.35%-1.0% (by volume). When viewed across the entire frequency spectrum, the conductivity and dielectric constant frequency dispersions reveal two regions of relaxation. The definition of these regions becomes more pronounced as the fiber dosage is increased. It is proposed that the low frequency relaxation process (1 Hz-1 kHz) is related to the enhanced charge transfer characteristics at the electrode-material interface produced by the presence of the carbon fibers in the vicinity of the electrodes. The high frequency relaxation process (5 kHz-10 MHz) results from a Maxwell-Wagner effect produced by the presence of highly conducting inclusions (the carbon fibers) in the low conductivity mortar matrix. © 2009 The American Ceramic Society.