A very low frequency (VLF) surface wave can propagate along the lower boundary of the ionosphere in the equatorial region. This was shown by a numerical simulation of the VLF field in the earth-ionosphere waveguide taking into account its anisotropy and using the realistic model of the electron density and collision frequency of the ionosphere. Calculations using the adiabatic approximation of the normal modes method show that the energy of the normal modes is trapped by the upper side of the waveguide. This effect becomes stronger near the geomagnetic equator and decreased with the distance to the equator, hence, the trapping effect is frequency dependent.