The dependencies of electrical conductivity on the electrical field and temperature of high-resistivity polystyrene/carbon nanotube (CNT) composites were investigated. The electrical conductivity of the samples and their thermal activation energy were systematically dependent on the CNT doping level. Several unusual phenomena were observed which could be explained by the inhomogeneous distribution of CNTs in the polystyrene matrix. At higher levels of CNT doping, an interconnected conducting network is formed. If the amount of CNT is equal to or less than 0.6%, "islands" of CNT become separated by the layers of polystyrene, which limit charge transport. At low voltages, there is a sharper decrease in conductance as the voltage decreases.