There is contention in perceptual-motor research concerning the degree to which observing biological and non-biological movements have equivalent effects on movement production. This issue results from the proposal that action observation and production share neural resources (i.e., mirror neurons) particularly sensitive to actions performed by other agents (i.e., beings with goals/intentions). In support of this claim, several discrete and rhythmic action-observation studies found that action production is only affected when participants believed that observed actions were produced by an agent. Here we present data from two experiments investigating whether similar agency manipulations also affect spontaneous movement synchrony. Collectively, the results suggest that belief in the agency of an observed movement does not affect the emergence and stability of rhythmic movement synchrony. These results question whether the actions of other agents are truly privileged across all scales of coordinated activity, particularly with respect to the lawful dynamics underlying movement synchrony.