You can use WMI as following

strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate}!\\" & strComputer & "\root
\cimv2")

Set colComputer = objWMIService.ExecQuery _
("Select * from Win32_ComputerSystem")

For Each objComputer in colComputer
Wscript.Echo "Logged-on user: " & objComputer.UserName
Next