An experimental investigation is carried out on a system consisting of a primary structure coupled with a passive/active autoparametric vibration absorber. The primary structure consists of a building-like mechanical structure, it has three rigid floors connected by flexible columns made from aluminium strips, while the absorber consists of a cantilever beam with a PZT patch actuator actively controlled through an acquisition card. The whole system, which is a coupled non-linear oscillator, is subjected to sinusoidal excitation obtained from an electromechanical shaker in the neighborhood of internal resonances. The natural frequency of the absorber is tuned to be one-half of any of the natural frequencies of the main system. With the addition of a PZT actuator, the autoparametric vibration absorber is made active, thus enabling the possibility to control the effective stiffness associated to the passive absorber and, as a consequence, the implementation of an active vibration control scheme able to preserve, as possible, the autoparametric interaction as well as to compensate varying excitation frequencies. This active vibration absorber employs feedback information from an accelerometer on the primary structure, an accelerometer on the tip of the beam absorber and a strain gage on the base of the beam, feedforward information from the excitation force and on-line computations from the nonlinear approximate frequency response, parameterized in terms of a proportional gain provided by a voltage input to the PZT actuator, thus providing a mechanism to asymptotically track an optimal, robust and stable attenuation solution on the primary system.