The dual mechanisms of control framework postulates that cognitive control can operate in 2 distinct modes: a "proactive" preparatory mode and a "reactive" wait-and-see mode. Importantly, the 2 modes are associated with both costs and benefits in cognitive performance. Here we explore this framework, in terms of its relationship with working memory capacity (WMC). We hypothesize that high-WMC individuals are more likely to utilize proactive control yielding not only benefits, but also specific costs to performance. Across 2 separate, large-sample experiments, healthy young adults performed different variants of the AX-Continuous Performance Test context processing task, a well-established probe of proactive and reactive cognitive control. In 2 experiments, WMC predicted both improvements and relative impairments in task performance in a manner that was consistent with usage of proactive control. These findings suggest that individuals differ in the degree to which they utilize proactive control based on WMC.