We consider a random scheduling problem for OFDMA-based indoor PLC systems with time- and frequencyvarying channel conditions in a multiuser context. In multichannel systems, opportunistic scheduling can exploit multiuser diversity in both time and frequency domains to improve the system performance. On the other hand, designing a scheduling scheme that simultaneously attains high performance and coordinates different users to share the channel fairly, especially over short time scales, is a challenging problem. In this paper, we propose an efficient opportunistic random access MAC protocol with short-term fairness constraint for OFDMA-based indoor PLC networks. Contrary to the conventional CSMA/CA, the proposed MAC protocol opportunistically adjusts the backoff time of each user based on the knowledge of channel state variations, and thus ’better’ users are more likely to access the channel. In addition, users that are involved in collisions and fail to contend during backoff process because there is no available subchannels are assigned higher priority in the following contention period to achieve a tradeoff between high throughput and shortterm fairness. Simulation results demonstrate that the proposed protocol provides significant improvement in system throughput and short-term fairness.