We have developed a numerical method for calculating the motion of toner and carrier particles in an electrophotographic two-component magnetic brush development system by using a three-dimensional distinct element method. A characteristic feature of this simulation method is that forces applied to toner and carrier particles include not only magnetic but also electrostatic forces involving a time-dependent electric current in the brush of conductive carrier particles. A parallelization technique for numerical computation was adopted in order to reduce the calculation time. The calculation results qualitatively agreed with the experimental observations in that the number of developed toner particles increases with the development voltage, as well as that some carrier particles adhere to the surface of the photoreceptor drum upon application of high development voltage. It is expected that the presented numerical method can be utilized for the improvement of the two-component magnetic brush development system in electrophotography.