Sì, è possibile e si può fare in svariati modi.

Qui uno tra tanti:
codice:
<!DOCTYPE HTML>
<html>
  <head>
    <title>Esempio</title>
    <meta charset="utf-8">
  </head>
  <body>
        
        <input type="text" id="id1_required" value="" name="id1">
        <input type="text" id="id2_required" value="" name="id2">
        <input type="text" id="id3_required" value="" name="id3">
        
        <fieldset id="tuofieldset" disabled='disabled'> <input><input><input>... </fieldset>
        
    <script type="text/javascript">
            var required = document.querySelectorAll("#id1_required, #id2_required, #id3_required");
            required[0].onchange = required[1].onchange = required[2].onchange = attivaFieldset;
            function attivaFieldset(){
                document.getElementById("tuofieldset").disabled = (required[0].value == "" || required[1].value == "" || required[2].value == "" );
            }
            attivaFieldset();
    </script>        
        
  </body>
</html>