In many real time applications, security is an important requirement, since the system maintains sensitive information to be shared by multiple users with different security levels. A secure real-time database system must satisfy not only logical data consistency but also the timing constraints and security requirements associated with transactions. Even though an optimistic concurrency control method outperforms locking based methods in firm real-time database systems, in which late transactions are immediately discarded, existing secure real-time concurrency control methods are mostly based on locking. In this paper, we propose a new optimistic concurrency control protocol for secure real-time database systems. We also compare the performance characteristics of our protocol with locking based methods while varying workloads. The results show that optimistic concurrency control performs well over a wide range of system loading and resource availability conditions.,