Our objective was to use computational modeling to provide a full and comprehensible physical description of the electrical and thermal behavior during electroencephalography-guided radiofrequency thermocoagulation (SEEGRF-TC), a minimally invasive procedure to destroy epileptic foci in the brain. We used the Finite Element Method to solve a coupled electrical-thermal problem and obtain the temperature distributions in the tissue for a constant power thermocoagulation. We found that 5 W provokes an impedance roll-off (abrupt increase) after approximately 10 s, and that this is related to temperatures of 100 degrees C in the surroundings of the contacts. Due to the internal resistance associated with the wires of the electrode, self-heating provoked a temperature increase of up to 3.3 degrees C throughout the device. Our findings should alert clinicians who are guided by impedance during SEEG-RF-TC regarding overheating associated with roll-off. The self-heating (approximately 3 degrees C) occurring along the electrode should also be taken into account as it could provoke thermal side-effects.