The paper deals with some computational aspects of modeling the lightning return strokes using the full wave model. The electromagnetic model of lightning return stroke is based on the thin wire antenna theory and the related Pocklington integro-differential equation in the frequency domain while the corresponding transient response is obtained by means of hybrid (analytical and numerical) version of the Inverse Fourier Transform. The Pocklington equation is solved by the Galerkin-Bubnov Indirect Boundary Element Method (GB-IBEM). Special attention is given to the computational differences arising from the usage of current and voltage source, respectively.