This paper presents an optimal amplify-and-forward (AF) relay scheme for a multiple-input-multiple-output (MIMO) system consisting of M-mobile sources, M-mobile destinations, and N-cooperative distributed mobile relay nodes. A wireless mobile relaying network with channel state information is investigated. The received signals from the mobile sources are exchanged between mobile relays to achieve optimal performance. The main contribution in this paper is the derivation of mobile relaying amplifying matrices (MARMs) designed for cooperative MIMO networks based on the minimum mean square error (MMSE) criterion. By adopting the new proposed MRAMs, the bite error rate (BER) performance of the system is evaluated using Monte-Carlo simulations.