The stars of the middle main sequence often have spot-like chemical structures at their surfaces. We consider diffusion caused by electric currents and argue that such current-driven diffusion can form chemical in homogeneities in plasma. Diffusion was considered using partial momentum equations derived by the Chapman-Enskog method. We argue that diffusion caused by electric currents can substantially change the surface chemistry of stars and form spotted chemical structures even in a relatively weak magnetic field. The considered mechanism can be responsible for a formation of element spots in Hg-Mn and Ap-stars. Diffusion in the presence of electric currents can be accompanied by propagation of a particular type of magneto hydrodynamic modes in which only the impurity number density oscillate. Such modes exist if the magnetic pressure is much greater than the gas pressure and can be the reason of variations of the abundance peculiarities in stars.