Hi All,
Today I am sharing my old script that I had used for updating the group members from CSV file.
I was performing the same activity today so thought of sharing it.
You just have to Prepare CSV as below:-

after that just define group name inside the script.
#############################
$grp =
##############################
This script requires quest management shell.
http://www.quest.com/powershell/activeroles-server.aspx
Execute script as below:

below is the link to the zip file along with script & example csv
http://gallery.technet.microsoft.com/scriptcenter/Update-Group-Members-from-46e27c78
Script Code:-
###########################################################################################
##
## Author: Vikas Sukhija
## Date: 26-11-2012
## Description:- If user is not a member of group this script add it after reading
## from CSV
###########################################################################################
#Add Quest Shell...
If ((Get-PSSnapin | where {$_.Name -match "Quest.ActiveRoles"}) -eq $null)
{
Add-PSSnapin Quest.ActiveRoles.ADManagement
}
#####define Group########
$grp="Group Name"
#########################
# import csv file
$data = import-csv $args[0]
$Can = “CN=$grp”
Write-host $Can
#Check if usr belogs to group in csv
foreach ($i in $data)
{
$user=get-qaduser $i.userid
if (($user.memberof -like “$Can,*”))
{
write-host “$user is a member & will not be added to $grp group”
}
else
{
write-host “$user is not a member & will be added to $grp group”
add-qadgroupmember $grp $user
}
}
########################################################################################
Regards
Sukhija Vikas