Previous research has indicated that caffeine exerts positive effects on various cognitive and behavioural processes, particularly reaction time, vigilance and arousal, and especially in sub-optimal conditions when arousal is low. However, it remains uncertain whether caffeine exerts any discreet effects on early cognitive processes, rather than a general effect on arousal and attention. The present study examined whether acute administration of caffeine modulates automatic auditory stimulus discrimination as measured by the mismatch negativity (MMN) event-related potential (ERP). As the MMN is attention-independent, modulation of the MMN by caffeine can be distinguished from a change in attention and arousal. ERP responses to tone duration deviants were recorded at baseline and following a cup of coffee with caffeine (200 mg) or decaffeinated coffee in a crossover study of 39 healthy older participants. No effect of Treatment was observed on the mean MMN amplitude at frontal electrodes, suggesting that caffeine has no effect on the brain’s automatic, preconscious auditory change detection system.