Although carbon nanofibers might have wide potentials in applications, most of their physical properties have yet to be investigated. This paper reports on the low-temperature electronic transport properties of an electrospun polyacrylonitrile-based carbon nanofiber, with its mean diameters around 120 nm. The resistance of the carbon fiber was measured using the four-point probe method from 295 down to 15 K. The semiconducting nature of the fiber is revealed by its positive temperature coefficient of conductance, i.e., an increase in conductivity with the temperature. The conductivity (sigma) depends on temperature according to the relation, sigma = 5768 T-0.338 exp(-2 x 10(-6) eV/kT), suggesting an almost zero bandgap and a strong temperature dependence of carriers mobility. Such temperature dependence of conductivity is very similar to that found in carbon microfibers, and can be explained using a simple two-band model with temperature-dependent mobility.