The electrical response of thermoplastic composites composed of carbon black and high-density polyethylene near the electrical percolation threshold (p(c)) has been investigated through the study of the volume resistivity and complex permittivity. The change in conductivity beyond p(c) exhibited a critical exponent that was greater than predicted from percolation theory. Composites with carbon black contents slightly larger than p(c) exhibited the greatest sensitivity in volume resistivity with temperature variations under the melting point of polyethylene. In addition, percolating composites with low carbon black contents exhibited significant "negative temperature coefficient" (NTC) effects and improvements in conductivity with annealing. Maxwell-Wagner interfacial polarization resulted in moderate increases in both the permittivity (epsilon') and dielectric loss factor (epsilon ") below p(c), while at percolation, an abrupt and dramatic increase was observed for both components of the complex permittivity.