My Yahoo finance stock sreen refreshes itself few times (About 5 to 6). For example link http://finance.yahoo.com/q?s=goog Dose any one knows why so ?

Yes, the feature of yahoo finance will refresh your page automatically so you can get the most up to day information. I think it is a nice feature. See http://ibooyah.com for stock analysis.

It continues to update while the stock prices are changing. It will do this as long as the market is open. I think you can turn off that feature if you want to.