A transmission output restricting method and apparatus of a portable terminal includes a radio frequency (RF) unit to detect a transmission power reflected based on a degree of mismatching of an antenna when a transmission power is emitted via the antenna, and to measure a transmission power increased due to the reflected transmission power caused by a human contact to the antenna, and a controller to control an output of the transmission power by restricting the output of the transmission power when the transmission power measured by the RF unit is greater than or equal to a predetermined value.