This study examined the effects of test anxiety on working memory capacity. Studies have demonstrated that individuals with trait social anxiety disorder exhibit increased visual working memory capacity and that those with trait anxiety exhibit decreased working memory capacity. Test anxiety may also induce unique effects on individuals' working memory capacity, and we thus employed the change detection task to explore such effects. Participants were divided into high- and low-test anxiety groups. We used K score and contralateral delay activity (CDA) amplitude to measure working memory capacity, focusing on processing effectiveness and efficiency. The study results revealed that deficits in the working memory capacity of individuals in the high test anxiety group manifested in the CDA amplitude rather than in the K score. The CDA amplitude of the high test anxiety group did not increase after load 3, and that of the low test anxiety group did not increase after load 4. No difference was observed in the K scores of the two groups. The study concluded that test anxiety impairs processing efficiency but not processing effectiveness.