You can do that by drawing the circle in a picture indicator using "Draw Circle by Radius.vi", located in:
Diagram palette -> Graphics & Sound -> Pictures Functions
Use the "Pixel Center" to locate the circle in the picture indicator.
I attached a VI in which you can locate a circle at run-time in a picture indicator by moving two slide controls: one for the vertical and one for the horizontal position. You can also change the radius of the circle and if you want to fill the circle.
The vi was written in LabVIEW 6.
Regards;
Enrique
www.vartortech.com