An important cognitive function underlying unified, voluntary behavior is attentional control. Two frontal regions, anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC), appear to be particularly involved in attentional control and monitoring. In this study, we investigated whether ACC is involved in monitoring the preparatory allocation of attention during task switching, or whether ACC is active only when subjects are processing target stimuli and selecting a response, via a cued-attention design. Event-related BOLD fMRI activity was examined using a cue-target paradigm in which subjects performed task switches that selectively required reallocation of attention when tasks changed. There were three cue conditions: informative switch, informative repeat, and neutral. There were four target conditions: informatively cued switch, informatively cued repeat, neutrally cued switch, and neutrally cued repeat. Significant ACC activity was observed following both informative switch and informative repeat cues, but not after neutral cues. No significant ACC activity was observed following any of the target conditions. Significant DLPFC activity was observed following all three cue conditions and following neutrally cued switch targets. Overall, our results suggest that ACC is involved in monitoring the preparatory allocation of attention for conflict at the level of activation of competing attentional sets. The results also support the role of DLPFC in holding cognitive goals in working memory and allocating attention to the appropriate processing systems to meet those goals.