Yes, you can uninstall it because Microsoft Office Activation Assistant is a tool that allows customers who have Microsoft Office 2007 pre-installed to activate their product. Once you activate the package, you don't need the application anymore. However it is a small utility which doesn't require much space or resources.
To uninstall it, you can use the uninstaller from the installation folder or Add or Remove Programs feature:
If you use Windows XP or bellow you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the program and then click Remove.
If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the application and click on Uninstall.