According to an aspect of the present disclosure, an access point sends timing information related to updating of a group key. A wireless station communicates with the access point according to the timing information to receive an updated group key. The updated group key is thereafter used for processing of multicast packets. Due to the use of the timing information, the wireless station can operate in a power-down mode, and yet receive at least the required group keys. In one embodiment, the timing information specifies a future time instance at which the update group may be available. In an alternative embodiment, a version number is associated with each value of the group key and the version number of the currently operative group key (in the access point) is broadcast to the wireless stations.