Higher bit rates and enhanced reception are required by the next generation communication systems to sustain multimedia traffic and this stimulates the researchers to work on technologies that can fulfil these requirements. One of the most successful technologies that have emerged is Multicarrier Code Division Multiple Access (MC-CDMA). Moreover with space time block coding (STBC) technique, MC-CDMA systems can have an added merit of transmit diversity. In this paper, we have developed an STBC MC-CDMA system and evaluated it for Multiple access interference (MAI) based on different spreading codes. We have employed three spreading codes namely orthogonal Gold code, Walsh Hadamard code and orthogonal complementary sequence. We have compared the performance of these codes in both 64 and 128 subcarrier systems and find that the orthogonal complementary sequence performs better than the other two in both the scenarios.