Carbon nitride (CNx) films have been deposited with an opposed-targct Penning-type sputtering source. The DC resistivity of films with different nitrogen content has been investigated using the four-point probe method and van der Pauw structures. The resistivity of nitrogen containing films is considerably higher than nitrogen-free films. From temperature-dependent resistivity measurements, the activation energy was found to increase with nitrogen content and from optical absorption measurements, the optical band,gap was calculated as 0.4 eV for pure carbon films and small gaps ( similar to 0.1 eV) were found for nitrogen containing films. The resistivity and the refractive index of the films was found to correlate with the C=N bond density.