Problems with ajax.beginform and client side validation

I want to do validations on the client side but I run into the following problem. If the model is not valid, I will return the view with the error messages in UpdateTargetId of the form, so that:

The part of the code of the form would be the following:

@using (Ajax.BeginForm("Index", "Estadistica",
                    new AjaxOptions
                    {
                        OnBegin = "onBegin",
                        OnComplete = "onComplete",
                        OnFailure = "onSuccess",
                        OnSuccess = "onFailure",
                        HttpMethod = "Post",
                        InsertionMode = InsertionMode.Replace,
                        UpdateTargetId = "dvAjaxFormResult"
                    }))
                {...}

The driver code is as follows:

 public ActionResult Index()
    {
        if (!(Session["Usuario"] is Usuario))
        {
            return RedirectToAction("Index", "Login");
        }

        var modelo = new EstadisticaIndex
        {
            FechaDesde = DateTime.Now.Date,
            FechaHasta = DateTime.Now.Date,
            Regional = Funciones.ListaRegional()
        };
        return PartialView(modelo);
    }

    [HttpPost]
    public ActionResult Index(EstadisticaIndex filtroEstadistica)
    {
        if (!(Session["Usuario"] is Usuario))
        {
            return RedirectToAction("Index", "Login");
        }
        var modelo = new EstadisticaIndex
        {
            FechaDesde = DateTime.Now.Date,
            FechaHasta = DateTime.Now.Date,
            Regional = Funciones.ListaRegional()
        };

        if (!ModelState.IsValid)
        {
            return PartialView(modelo);
        }
        return RedirectToAction("EstadisticaConsecutivos", "Estadistica",filtroEstadistica);


    }