Probably not. It may be that you have set the font size in your browser, or have changed the resolution on your monitor. More likely is the first case, because that can sometimes easily be done without noticing.
If you're using Internet Explorer, in the view menu, choose Text Size then Medium
If you're using Firefox or Netscape 8.0, in the view menu, choose Text Size, then Normal.
If you're using Netscape 7.x, in the view menu, choose Text Zoom, then 100%.