PowerShell function :: Check if domain-joined computer is a member of AD group, without AD module.

ComputerIsInGroup.ps1

function ComputerIsInGroup {
	param (
		[Parameter(Mandatory=$True)]
		[string]$GroupName
	)

	# Get computer's DN
	$objSearcher = New-Object System.DirectoryServices.DirectorySearcher
	$objSearcher.SearchRoot = New-Object System.DirectoryServices.DirectoryEntry
	$objSearcher.Filter = "(&(objectCategory=Computer)(SamAccountname=$($env:COMPUTERNAME)`$))"
	$objSearcher.SearchScope = "Subtree"
	$obj = $objSearcher.FindOne()
	$computer = $obj.Properties["distinguishedname"]

	# Now get the members of the group
	$objSearcher.Filter = "(&(objectCategory=group)(SamAccountname=$GroupName))"
	$objSearcher.SearchScope = "Subtree"
	$obj = $objSearcher.FindOne()
	[String[]]$members = $obj.Properties["member"]

	return ($members -contains $computer)
}

# Example usage:
# If (ComputerIsInGroup "Workstations") { Write-Host 'Computer is a member.' } else { Write-Host 'Computer is Not a member.' }