The aftereffects of prospective memory (PM) are a phenomenon by which, after the completion or cancellation of a PM task, the intention remains active. The current study investigates the effect of task difficulty on the aftereffects of PM. In Experiment 1, 132 college students were recruited to explore the effect of ongoing task difficulty on the aftereffects of PM. The results of one-way analysis of variance (ANOVA) showed that the commission error rate under the high-difficulty condition was higher than that under the low-difficulty condition. In Experiment 2, 105 college students were recruited to further investigate the effect of prospective memory task difficulty on the aftereffects of PM. The results of one-way ANOVA showed that the commission error rate under the single cue condition was higher than that under the multiple cues condition. The results of the above two experiments indicate that PM aftereffects are easily influenced by task difficulty, which suggests that the PM aftereffects involve controlled processing. The results of this study tested multiple conflicting theoretical viewpoints, which is beneficial for confirming the processing mechanism of PM aftereffects. This study has been registered and the registration number is ChiCTR2500098910.