You could remove the MouseListener that JCheckBox has that gives it this behavior:
JCheckBox checkBox = new JCheckBox("Check Box");
EventListener[] listeners = checkBox.getListeners(MouseListener.class);
for (EventListener eventListener : listeners) {
checkBox.removeMouseListener((MouseListener) eventListener);
}
Also consider setting the JCheckBox's focusable property to false:
checkBox.setFocusable(false);
This prevents the user from tabbing to the check box and then toggling its state with the space bar.