Percutaneous RF ablation is one of alternative treatment for non-surgical liver tumors. Ablative changes in hepatic tissue can be successfully estimated using the finite element method. The authors created a 3D model of a multi-tine applicator immersed in liver tissue, and then determined the optimal values of voltage applied to such an RF electrode, which do not exceed the therapeutic temperature range valid during thermal ablation procedure. Importantly, the simulations were carried out for the RF electric probes with 2 to 5 evenly spaced arms. Additionally, the thermal damage of hepatic tissue for multi-armed applicators working at pre-defined limit values of voltages was established based on the Arrhenius model.