A method and apparatus are disclosed from the perspective of a UE (User Equipment). In one embodiment, the method includes the UE receiving a first MAC-CE (Medium Access Control-Control Element) including or indicating a plurality of TCI (Transmission Configuration Indication) state IDs (Identities) to be activated for receiving PDSCH (Physical Downlink Shared Channel), wherein format of the first MAC-CE depends on amount of the plurality of TCI state IDs. The method further includes the UE activating a plurality of TCI states associated with the plurality of TCI state IDs included or indicated in the first MAC-CE for receiving the PDSCH in response to reception of the first MAC-CE.