The concept of secure group communication (SGC) has recently appeared in the filed of wireless sensor networks (WSNs). To design a dynamic, efficient, and secure group access control scheme is one of the essential issues. Although several studies have made progress in terms of access control, their methods are inadequate for SGC-based WSNs. This paper proposes a dynamic access control scheme (DACS), which can fulfill the requirements of dynamic, efficiency, and security. Specifically, the DACS offers the following advantages. Every sensor node needs to compute hash computation only once and then can obtain the corresponding group access key, whether in the initialization or in the maintenance. In addition, the task manager (i.e., the administrator) can flexibly generate the secure filter function for every entity (i.e., the sensor nodes or other devices) to derive the corresponding group access key, regardless of whether the relation among entities is hierarchical or horizontal.