In this paper, we introduce a proposed scheme to enhance the performance of orthogonal space time block code (OSTBC) with four time slots and two antennas for by combing OSTBC with random beamforming. Multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system has been recognized as one of the most promising techniques to achieve a good service and increase data rate in the next generation (4&5G) broad band wireless communications. So, we apply Space time block code (STBC) for MIMO-OFDM system with linear decoding. Also, we perform STBC with beamforming for MIMO-OFDM system. Simulation results show that the beamforming improves bit error rate (BER) performance of OSTBC and STBC-OFDM for different types of modulation and diversity.