Method and apparatus for handling upon UL timing asynchronism in a wireless communication system are disclosed herein. The user equipment (UE) maintains a timing advance (TA) value for each of a plurality of beams used for uplink transmissions to a cell, or a transmitter/reception point (TRP) operatively connected to a gNodeB (902). If less than all of the maintained TA values become invalid, then the UE will continue transmission on any beam for which the TA value remains valid, while discontinuing transmission on any beam with an invalid TA value (904).