A touch screen system, comprising: a touch screen panel comprising a plurality of driving lines and a plurality of sensing lines crossing the driving lines, and a plurality of sensing cells being formed at crossing regions of the driving lines and the sensing lines; a driving circuit for sequentially applying driving signals to the driving lines wherein when the driving signal is provided to one of the driving lines, the other driving lines are grounded; a sensing circuit for detecting first sensing signals in accordance with changes in mutual capacitances of the sensing cells to generate second sensing signals corresponding to the changes; a processor for determining a touch position based on the second sensing signals from the sensing circuit; and an active stylus separated from the touch screen panel and comprising: a signal generator configured to generate a signal in accordance with the electric field generated by the driving signal; an electric field emitter configured to amplify the signal generated by the signal generator to output an active stylus electric field; and a power source configured to supply power to the signal generator and the electric field emitter; an electric field sensor configured to sense an electric field generated by the driving signal applied to a driving line that makes contact with or is approached by the active stylus, wherein the signal generator is configured to generate the signal when the electric field is sensed by the electric field sensor and does not generate the signal when the electric field is not sensed by the electric field sensor, such that the signal generator only generates the signal when the driving signal is applied to the driving line that makes contact with or is approached by the active stylus, and does not generate the signal when the driving signal is not applied to the driving line that makes contact with or is approached by the active stylus. a touch screen panel comprising a plurality of driving lines and a plurality of sensing lines crossing the driving lines, and a plurality of sensing cells being formed at crossing regions of the driving lines and the sensing lines; a driving circuit for sequentially applying driving signals to the driving lines wherein when the driving signal is provided to one of the driving lines, the other driving lines are grounded; a sensing circuit for detecting first sensing signals in accordance with changes in mutual capacitances of the sensing cells to generate second sensing signals corresponding to the changes; a processor for determining a touch position based on the second sensing signals from the sensing circuit; and an active stylus separated from the touch screen panel and comprising: a signal generator configured to generate a signal in accordance with the electric field generated by the driving signal; an electric field emitter configured to amplify the signal generated by the signal generator to output an active stylus electric field; and a power source configured to supply power to the signal generator and the electric field emitter; a signal generator configured to generate a signal in accordance with the electric field generated by the driving signal; an electric field emitter configured to amplify the signal generated by the signal generator to output an active stylus electric field; and a power source configured to supply power to the signal generator and the electric field emitter;