To prevent Electric shock, an alternating frequency that is higher than power from standard wall outlets is used. Normal "house-current" AC runs at 50-60 Hz and is quite lethal, since at every alteration nerves and muscles get stimulated, causing violent cramps 50-60 times a second. However, nerve and muscle stimulation cease at 100,000 Hz due to alterations being too fast for the cells to pick up. Electrosurgery can be performed safely at “radio” frequencies above 100 kHz.
http://en.wikipedia.org/wiki/Cauterization#Electrosurgical_Generator_.28ESG.29