On autopostback, dropdown list selected index is going back to '0' in ASP.Net MVC3

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ASP.NET

MVC

Hi all,
On autopostback, dropdown list selected index is going back to '0'. How to maintain to not go to zero in MVC3.
My code is
View is:

@using (Html.BeginForm())
{
    @Html.ValidationSummary(true)
    <div>
        <div style="float: left">
            States Filter :</div>
        <div style="float: left; padding-removed 20px">@Html.DropDownList("Areas", ViewData["Areas"] as SelectList, "-select state-", new {@style = "width:200px;" })</div>
    </div>
    <div style=" padding-removed30px">
        
            <input type="image" value="submit" src="../../Images/FilterBrowse.gif" alt="submit Button"  />
        
    </div>
    
}
for each loop table(Gridview)

Controller is:

//[Authorize]
        public ActionResult States()//int? id)
        {
            ViewData["Areas"] = new SelectList(am.FindUpcomingStates222().ToList(), "state_Name", "state_Name");
            var state = am.FindUpcomingStates().ToList();
            if (state != null)
            {
                ViewData["name"] = true;
                return View("States", state);
            }
            else
                return View("NotFound");
        }


[AcceptVerbs(HttpVerbs.Post)]
        public ActionResult States(string _stateName, FormCollection formvalues)
        {
            _stateName = Request.Form["Areas"].ToString();
            ViewData["Areas"] = new SelectList(am.FindUpcomingStates222().ToList(), "state_Name", "state_Name", _stateName);
            if (_stateName == "")
            {                
                return View();
            }
            else
            {                
                var state = am.FindUpcomingStates22(_stateName).ToList();
                if (state != null)
                    return View("States", state);
                else
                    return View("NotFound");
            }
        }

after clicking submit button ddl going to selected index zero
Thanks,
Sampath bejugama