FDTD and Monte Carlo methods are combined to simulate the terahertz radiation from a coplanar photoconducting structure. The simulation tool under consideration allows calculation of potentials, particle distributions, current densities, and the near field electromagnetic fields anywhere in the computational domain. To model the far field radiation, it is not efficient nor, in many cases, physically possible at present to use the FDTD technique directly because of the excessive computational burden. Techniques are discussed for modeling both the near field and the far field radiation. Computational results showing the far field radiation are in qualitative agreement with published experimental results.