Android alertdialog from a menu selection

How to pop up a dialog from a menu selection

 @Override
    public boolean onOptionsItemSelected(MenuItem item) {
         switch(item.getItemId()) {
          case (MENU_ABOUT): {         
                new AlertDialog.Builder(this)
                .setTitle("About Mala Counter")
                .setMessage("Version 1.0 from Cubicware.com")
                .setPositiveButton(android.R.string.ok, null)
                .show();
                return true;
          }
         }
         return false;
    }