Electrical conductivity of polyester filled with carbon nanotubes composites have been studied from 240 to 380 K in the frequency range from 100 Hz to 1 MHz as a function of the filler volume fraction above the percolation threshold. The frequency dependence of the electrical conductivity obeys the universal dynamic response. Positive temperature coefficient in resistivity and negative temperature coefficient in resistivity phenomena were observed at temperatures below and above the glass transition respectively. It was found that the mechanism responsible for the changes in resistivity is predominantly due to the tunneling effect. Positive temperature coefficient in resistivity intensity was also exploited which is strongly dependent on the carbon nanotube content.