In this paper, we have applied the finite difference time domain (FDTD) method and the first order Mur boundary condition for calculating the electromagnetic (EM) by solving Maxwell’s curl equations in three dimensions (3D) to study the EM propagation inside a dielectric medium in 3D and the calculations were performed using MATLAB. This study presented many numerical solutions to make a comparison between the calculations. The results clearly indicated that the slab can be utilized to control the direction of the EM propagation. The calculations demonstrated that the electromagnetic waves propagated and the maximum of the electromagnetic fields was concentrated inside the dielectric by the total internal reflections. The EM waves bilaterally propagated once the source is located in the middle of the slab. The EM waves can be produced 90 degree out of phase when the results are compared with each other. The calculations have verified that the distributions of the fields should be affected when the source setting changes, as the sources assigned to the electric component in the x-direction compared with y-direction. The final, two numerical solutions can be compared. The first one, the source was placed inside a dielectric which can be compared to the source being placed in free space. The results from the first calculation showed that the dielectric controls the propagation direction of the EM waves while the second solution demonstrates that the electromagnetic scattered by a dielectric............... Key words:............ finite difference time domain (FDTD) method, Maxwell’s curl equations, absorbing boundary condition (ABC), three dimensions (3D) system.