Actually the default culture do not recognize dd/mm/yyyy as date format. So first convert it to valid datetime as i shown then compare
using System.Globalization;
DateTime dt = DateTime.ParseExact(tbxFromDate.Value, "dd/MM/yyyy", CultureInfo.InvariantCulture);
if (tbxFromDate.Value != "" && dt > DateTime.Today)
{
Messagebox.Show("From Date should be earlier or equal To Today Date", MessageHelper.MessageType.Warning);
}