This study explores the use of a linear PMDC machine as a regenerative force actuator for the mitigation of earthquake disturbances in civil structures. Unlike previous studies of this kind, the control system developed is purely active, meaning no 'hybrid' control techniques are used, such as the combination of active force actuation and passive tuned mass dampers. Modeling methods for the machine as well as its associate drive electronics are briefly described. It is shown that for this purely active system, it is possible and feasible to develop regenerative excitation schemes which drive the machine primarily by absorbing power from the excited building. Such regenerative excitation makes it possible to isolate the actuator from the external power grid, which is necessary during earthquakes, where the quality, or even the mere availability of external power is questionable. Furthermore, results are presented which find the minimum reservoir of energy necessary to excite the machine during the beginning of the earthquake, and it is shown that the actuator local power supply will see a gain in energy across the duration of the disturbance. The control system design methods presented employ position feedback. Then, force limiting techniques are employed to regulate power flow in the machine. The effectiveness of this control design is evaluated on a 3-story building, and performance is briefly compared to that of semi-active control designs proposed elsewhere.