This paper presents the calculation of electric and magnetic fields produced by lightning striking over different configurations of nonflat lossy ground. The computation is performed using finite-difference time domain (FDTD) methods in two-dimensional (2-D) with cylindrical coordinate systems and 3-D with Cartesian coordinates. The FDTD method is validated with several previous approximations for lightning electric field computation, such as Uman equations and simulation of lightning striking on the top of a tower. In this study, it is found that lightning striking on the top of a cone-shaped mountain may produce several variations on an electromagnetic field. An enhancement of the perpendicular and parallel to ground electric field components was observed for a cone-shaped configuration only. For configurations that include flat planes, wave reflections due to the transition between the cone-shaped and flat plane were observed.