This paper presents the dynamic analysis of a linear isolator under active stiffness control. Firstly, the literature review on the active stiffness and the concept of skyhook spring are presented. Then, based on the theoretical equation govern the isolation system model, the effect of active stiffness control in the absolute motion transmissibility performance is studied. In addition, the force response of the isolation system under active stiffness control is also examined to highlight its benefits in improving the isolation system performance.