A method and apparatus are disclosed from the perspective of a UE. In one embodiment, the method includes monitoring a control channel for detection of an UL grant. The method further includes receiving the UL grant associated with a HARQ process on the control channel at a first timing. The method also includes sending an UL data associated with the UL grant on a data channel at a second timing. In additional, the method also includes starting a retransmission timer associated with the HARQ process after detection of the UL grant at a third timing. Furthermore, the method includes receiving a signaling indicating stop the retransmission timer at a fourth timing. In addition, the method includes stopping the retransmission timer and stopping monitoring the control channel, wherein the UE monitors the control channel when the retransmission timer is running.