The electric permittivity measurements under different ac or dc field amplitudes on lead-free (Na_0.5Bi_0.5)_0.88Ba_0.12TiO₃ ceramics were performed. A significant increase or decrease in permittivities was observed with increasing ac or dc fields intensity, respectively. It was found that temperature T_m decreases or increases with increasing ac or dc fields, respectively. When ac field amplitude increased, stronger frequency relaxation around T_m and greater shift in T_m was observed. This was in opposite to the effect of dc field intensity. The obtained results were discussed in terms of polar region behaviour in external electric fields.