The onset of convection in a porous medium saturated by a dielectric nanofluid with vertical AC electric field is investigated. The flux of volume fraction of a nanoparticle with the effect of thermophoresis is taken to be zero on the boundaries and the eigenvalue problem is solved using the Galerkin method. The model used for nanofluid incorporates the combined effect of Brownian diffusion, thermophoresis and electrophoresis, while for porous medium Darcy model is employed. The results show that increase in the AC electric Rayleigh-Darcy number, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh-Darcy number are to hasten the onset of convection. The size of convection cells does not depend on nanofluid parameters, but decreases with increasing the AC electric Rayleigh-Darcy number. The non-existence of oscillatory convection is also obtained.