You can activate your Origin Key via the Origin website, after downloading their PC app or via the Electronic Arts Website. 

Online Sign-in 

1. Select the My Game Library option and click on ADD A GAME option. Then click on Redeem Product Code. (This procedure also applies to the PC app) 
   
   
   
2. Enter your activation key in the dialog box and ensure that you’ve left no empty spaces before or after the code. 
   
   
   
3. Click on Next and enjoy gaming! 
   

EA Website

1. Log in to your account and go to the accounts page. 
   
   
   
2. Click on the Redeem Code option and enter your activation code. 
   
   
   
3. Click on Next and enjoy gaming!