If you would like force Windows activation upon the first boot into Windows following deployment, you can add the following tasks to your Answer File:
Phase: FIRST BOOT
Task 1 Command Line: cscript.exe "c:\windows\system32\slmgr.vbs /ipk xxxxx-xxxxx-xxxxx-xxxxx-xxxxx"
Task 2 Command Line: cscript.exe "c:\windows\system32\slmgr.vbs /ato”
Be sure to replace the xxxxx string with your actual product key. These tasks will first install the product key (/ipk) and then force activation (/ato)