JButton when clickedl leaves some border around text

JButton when clickedl leaves some border around text

I am having one simple form i created using JFrame.
In which i used one small JButton in which i set text only "X", now the
problem is that when i press that button some border appears around the
text which should not appear.
So, how can i resolve it?
How can i remove this border.I mean to say when the user clicks then also
it should not show this border.
Here Try to look at the button at the corner with red background.