You are instantiating two Dialogs. One AlertDialog and another DatePickerDialog. You should use only one:
@Override public Dialog onCreateDialog(Bundle savedInstanceState) {
final Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
DatePickerDialog dialog = new DatePickerDialog(getActivity(), this, year, month, day);
dialog.getDatePicker().setMinDate(c.getTimeInMillis() );
dialog.setButton(DialogInterface.BUTTON_NEUTRAL, "Today", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
query_date = now_date;
dialog.dismiss();
}
});
return dialog;
}