Micro-expression recognition is influenced by emotional contexts at the behavioral level. It is found that the recognition for micro-expressions is poorer following a negative context compared to the recognition following a neutral context. However, it remains unclear whether the modulation takes place in the early or later stage of the processing of micro-expressions as reflected in event-related potentials (ERPs). Using synthesized micro-expressions in this study, we investigated how emotional context modulates the ERP components that are elicited by micro-expressions. We observed that, compared to neutral contexts, negative and positive contexts elicited more positive amplitude trends for processing the subsequent target micro-expressions, and more positive P1 and N170 effects were elicited by target micro-expressions following negative and positive contexts compared to those following neutral contexts. Moreover, there were larger P1 effects elicited by the target micro-expressions when the context and target expressions were incongruent compared to when they were congruent. Our findings provide new ERP evidence to indicate that emotional contexts modulate micro-expression processing, and that the modulation of emotional contexts takes place at the early stage of facial-expression processing.