A method and apparatus are disclosed. In an example from the perspective of a User Equipment (UE), a signal to configure the UE to perform a Random Access Channel-less (RACH-less) handover to a second cell may be received in a first cell, wherein the signal comprises a candidate list of beams for Physical Downlink Control Channel (PDCCH) monitoring in the second cell and/or the signal is indicative of a first beam of the candidate list of beams (to be used by the UE for PDCCH monitoring). A PDCCH in the second cell on the first beam may be monitored before receiving a Medium Access Control (MAC) Control Element (CE) assigning a second beam for PDCCH monitoring in the second cell.