Active boring bars may be used for active vibration suppression during internal turning operation in metal cutting. This technique is based on a feedback control scheme of the boring bar vibrations measured by an attached sensor (usually accelerometer) where secondary "anti"- vibrations are applied by means of an embedded piezoelectric actuator. In order to design an active boring bar, several issues have to be addressed, i.e. selecting the characteristics of the actuator, the actuator size, the position of the actuator in the boring bar, etc. A mathematical model of the active boring bar incorporating the piezoelectric effect, e.g. a "3-D" finite element, may simplify designing process. In this paper several "3-D" finite element models of the system "boring bar - actuator - clamping house" are developed for a set of actuator positions. The favorable actuator position is basically selected as the one resulting in the greatest "stiffness" of the active boring bar at the frequency corresponding to the first boring bar fundamental bending mode.