Monitoring our performance is fundamental to motor control while monitoring other's performance is fundamental to social coordination. The striatum is hypothesized to play a role in action selection, action initiation, and action parsing, but we know little of its role in performance monitoring. Furthermore, the striatum contains neurons that respond to own and other's actions. Therefore, we asked if striatal neurons signal own and conspecific's performance errors. Two macaque monkeys sitting across a touch-sensitive table in plain view of each other took turns performing a simple motor task to obtain juice rewards while we recorded single striatal neurons from one monkey at a time. Both monkeys made more errors after individually making an error but made fewer errors after a conspecific error. Thus, monkeys' behavior was influenced by their own and their conspecific's past behavior. A population of striatal neurons responded to own and conspecific's performance errors independently of a negative reward prediction error signal. Overall, these data suggest that monkeys are influenced by social errors and that striatal neurons signal performance errors. These signals might be important for social coordination, observational learning and adjusting to an ever-changing social landscape.