A quote from steam product page "Online Disclaimer:.....REGISTRATION IS LIMITED TO ONE EA ACCOUNT PER SERIAL CODE, WHICH IS NON-TRANSFERABLE ONCE USED.......GAME CAN BE PLAYED ON UP TO FIVE COMPUTERS AT THE SAME TIME; USERS CAN MANAGE WHICH COMPUTERS ARE AUTHORIZED OR DE-AUTHORIZED TO PLAY GAME. VISIT http://activate.ea.com/deauthorize/ FOR MORE INFORMATION ON DE-AUTHORIZATION......."
[The EA support team can correct me if the information above is no longer relevant]
You can try to de-authorize the other copy if it is registered.