Due to electrokinetic effect in porous formation, an electromagnetic field as well as an acoustic field can be excited by an acoustic monopole source in a borehole. These fields are simulated and analyzed in this paper. The coupling between the acoustic field and the electromagnetic field in the porous formation is assumed to obey Pride's equations [Phys.Rev.B50:15678-15696 (1994)]. A magnetic field as well as an electric field accompanies the acoustic head wave, which travels with approximately the fast compressional wave velocity. It is shown that the head wave is not a pure fast compressional wave but a combination of different body waves. It is mainly the slow compressional wave constituent in the acoustic head wave that causes fluid filtration and radial electric field. Similarly, the fast and slow compressional wave constituents in the shear wave group cause electric field. Besides, there is an electric signal which arrives ahead of the acoustic head wave. This signal is shown to be the critically refracted radiating electromagnetic wave on the borehole wall by comparison between results from real axis integral and electromagnetic branch-cut integral.