It sounds like server side validation, so may be you can use client side validation features for this.
http://msdn.microsoft.com/en-us/library/gg508808(v=vs.98).aspx
In general, that may be done by using ajax call (not sure if you're using jQuery, but if not and there's no special limitations, would encourage to use it for this):
http://api.jquery.com/jQuery.ajax/
On client side:
$.ajax({
url: '@Url.Action("ActionName", "ControllerName")',
type: "POST",
async: true,
dataType: "json",
data: $('#form').serialize(),
success: function (data) {
// process result
},
error: function (request, status, error) {
// process error message
}
});
On server side:
[HttpPost]
public virtual ActionResult ActionName()
{
return Json("value")
}
But in general you should google from ASP.NET MVC 3 Ajax, there's plenty stuff regarding this in web and you may find exactly what you need already.