Special caracter is appearing in combobox like a "?"

Special caracter is appearing in combobox like a "?"

Dear friends,
 
I have here a jquery code that load one combobox to another with data from mysql. The point is, the combobox that receive the data from mysql, if I have a name with special caracter like "~" or "^" any other accent in the mysql, the combobox that receive this data appear a strange simbol like as in the file attached in the place of the letter that is with accent.
 
The code that I have here is
 
  1. $(document).ready(function(){       
          $("select[name=Empresas]").change(function(){
           $("select[name=Unidades]").html('<option value="0">Carregando...</option>');   
         $.post("unidades.php",
             {Empresas:$(this).val()},
             function(valor){
                $("select[name=Unidades]").html("<option>Selecione...</option>" + valor);
             }
             )   
          })      
       })









    2. Does anyone know how can I resolve this problem?
    Sorry about bad english, I´m from Brazil.