In this study, two instantaneous optimal control performance indices for seismic control of structures incorporating magneto-rheological (MR) dampers are analytically defined. One of the time dependent performance index uses conventional state vector considering simple soil structure interaction (SSI). However, absolute displacement and absolute velocities are added to the conventional state vector terms and eventually to the other one. SSI effects are also included simply in the second performance index. The response reduction performance of these simple indices is compared with the linear quadratic regulator control (LQR). A three story 1/4-scaled structure incorporating an MR damper is taken into account as a numerical example. The power requirement of the MR damper is considered by using an MR damper model which is piece wise invertible. It is obtained from numerical results that the proposed performance indices are as effective as LQR algorithm in uncontrolled seismic structural response reduction performance. However taking SSI effects into account increases structural responses and decreases control effectiveness slightly.