Altered postural control in people with chronic ankle instability (CAI) may be attributed to deficits that are associated with neurocognitive function. Acute training is another factor that may negatively affect postural control and increase the risk of ankle sprain. The purpose of this investigation was to determine the effect of acute exercise on postural stability and cognitive function among patients with CAI. Fifteen patients with CAI (aged 21.5 ± 2.0 years) and 15 healthy controls (aged 20.3 ± 1.7 years) completed a single-limb stance postural control test and a battery of computer-based cognitive tests before and after acute exercise. The overall stability index (OSI) was used as a measure of postural stability. The cognitive domains tested were global cognitive score, executive function, attention, visual-spatial perception, information processing, and fine motor control. Subjects in both groups had similar OSI scores, with a trend for reduced stability in the CAI after the exercise protocol (p = 0.053). There were no differences between the groups in all cognitive domains before or after exercise. Following exercise, the domains of overall cognitive score, visual-spatial perception, and information processing speed improved in both groups (p = 0.003, p = 0.033, p = 0.001; respectively). These findings should be considered with caution due to the heterogeneity of the CAI population.