We have recently reported that excitatory neurons in the claustrum mediate anxiety responses to acute psychological stressors that induce negative emotional states. However, it is unclear how claustral neurons represent information related to anxiety responses to a stressor. To address this question, here we performed calcium imaging of GCaMP6f-expressing claustral neurons in freely moving mice during three behavioral tests; the elevated plus maze, the open field test, and a second open field test after an exposure to a ten-minute single social defeat stress. Prior to exposure to a stressor, we found that a subset of claustral neurons displayed an increase in calcium levels upon transitioning to areas associated with increased anxiety in the elevated plus maze and the open field. In the open field test after exposure to social defeat stress, a different subset of neurons, including neurons that were activated by of stress, exhibited sustained high levels of calcium when entering and exiting the less anxiogenic corner zones of the open field. These results suggest that stress-related anxiety information is represented in a claustral neuronal population that is different from the population representing anxiety under non-stressed conditions.