A method and apparatus for testing operation of a random number generator (RNG) testing circuit are provided. In accordance with at least one embodiment, a first RNG output value obtained from a RNG is stored in a first register. In response to activation of a test mode to simulate a faulty RNG, the first RNG output value is stored in a second register. The first RNG output value in the first register is compared to the first RNG output value in the second register. In response to the comparing, a RNG failure signal is provided at a RNG testing circuit output of the RNG testing circuit. In accordance with at least one embodiment, sequential and combinational logic can simulate a faulty RNG. Accordingly, simulation of a faulty RNG may be performed to test a RNG testing circuit even when the RNG is not faulty.