Yes you can, use GPO to enabled the screen saver to come on and password protect...
Administrative Templates\Control Panel\Display...
Hide Screen Saver tab = Enabled
Password protect the screen saver = Enabled
Screen saver = Enabled
Screen Saver executable name = %windir%\system32\logon.scr
Screen saver timeout = 300
After 5 minutes, the screen saver will run and the logged on user will be asked for their password to unlock the machine..