The ultrafast electron transport is central to the requirement of all-electrically controlled spintronics in metallic collinear antiferromagnetic (AFM) Mn2Au thin films within the terahertz (THz) range. Here we use the THz time-domain spectroscopy to measure the conductivity spectra of Mn2Au thin films with different thicknesses and temperatures. We demonstrate an onset of carrier localization in Mn2Au with decreasing the film thickness from 15 to 5 nm. By using optical pump-THz probe spectroscopy, we found the surface trapping states in the thinnest Mn2Au film limit its photoconductivity significantly. The DC conductivity and scattering time become larger and longer with decreasing temperature for all samples, which suggests that Mn2Au behaves in a typical metallic fashion. The THz optical and conductivity properties of Mn2Au films will advance our understanding of ultrafast electronic transport processes in AFM Mn2Au thin films.