Numerical analysis of electric potentials and currents inside reinforced concrete is performed to study nondestructive evaluation of corrosion by the half-cell potential measurement and polarization resistance method. Electric fields around reinforcing steels are analyzed by using the Boundary Element Method (BEM). 3-dimensional analysis is conducted to compare with 2-dimensional analysis. In the polarization resistance method, the polarized area of rebar is associated with the current intensity on rebar, current ratio on rebar and the current flow from the counter electrode.