drawOval
accepts the top-left position and the width and height, not the centre position and the width and height.
It should be something like this:
public void paintComponent(Graphics g) {
super.paintComponents(g);
g.setColor(Color.BLUE);
g.drawOval(250 - radius, 250 - radius, radius * 2, radius * 2);
radius += 10;
if (radius + 10 < 250) {
paintComponent(g);
}
}