How does the brain maintain information in working memory while challenged by incoming distractions? Using functional magnetic resonance imaging (fMRI), we measured human brain activity during the memory delay of a spatial working memory task with distraction. We found that, in the prefrontal cortex (PFC), the magnitude of activity sustained throughout the memory delay was significantly higher on correct trials than it was on error trials. By contrast, the magnitude of sustained activity in posterior areas did not differ between correct and error trials. The correlation of activity between posterior areas was, however, associated with correct memory performance after distraction. On the basis of these findings, we propose that memory representations gain resistance against distraction during a period of active maintenance within working memory. This may be mediated by interactions between prefrontal and posterior areas.