In two ERP experiments, we examined whether active inhibition is involved in intentional forgetting. Both experiments consisted of a nondirected-forgetting (nDF) and a directed-forgetting (DF) block. Participants were sequentially presented with a prime, an R/F (remember/forget) cue, and a target. Participants made lexical decisions to both the primes and targets (Experiment 1) or only to the targets (Experiment 2). They were also instructed to remember or to forget the primes in response to the R/F cues in the DF block but to ignore these cues in the nDF block. The N400 semantic priming effect was observed when comparing the ERPs elicited by semantically unrelated and related targets in the DF block. In comparison to the nDF block, the N400 effect was greatly reduced for targets preceded by F cues in the DF block. These findings suggest that semantic processing is reduced by the instruction to forget and active inhibition is involved in intentional forgetting.