A method and apparatus are disclosed from the perspective of a User Equipment (UE). In one embodiment, the method includes the UE performing transmission and/or reception in a serving cell, wherein the serving cell is in unlicensed spectrum. The method further includes the UE being configured to receive slot format indication (SFI) on periodic SFI monitoring occasion(s), wherein periodic SFI monitoring occasion(s) is (pre-)configured by a network. The method also includes the UE, in response to receiving and/or detecting a channel indicator, monitoring and/or detecting a first SFI-related signal on a first occasion, wherein the first occasion is not one of (pre-)configured periodic SFI monitoring occasion(s).