Neuroimaging studies commonly show widespread activations in the prefrontal cortex during various forms of working memory and long-term memory tasks. However, the anterior prefrontal cortex (aPFC, Brodmann area 10) has been mainly associated with retrieval in episodic memory, and its role in working memory is less clear. We conducted an event-related functional magnetic resonance imaging study to examine brain activations in relation to recognition in a spatial delayed-recognition task. Similar to the results from previous findings, several frontal areas were strongly activated during the recognition phase of the task, including the aPFC, the lateral PFC and the anterior cingulate cortex. Although the aPFC was more active during the recognition phase, it was also active during the delay phase of the spatial working memory task. In addition, the aPFC showed greater activity in response to negative probes (non-targets) than to positive probes (targets). While our analyses focused on examining signal changes in the aPFC, other prefrontal regions showed similar effects and none of the areas were more active in response to the positive probes than to the negative probes. Our findings support the conclusion that the aPFC is involved in working memory and particularly in processes that distinguish target and non-target stimuli during recognition.