You can override the cordovaWebviewClient present in cordova lib and implement "onPageStarted" and "onPageFinished" methods. In pagestart make progress bar visiblity to visible and on page finish make it to gone.
public void onPageStarted(WebView view, String url, Bitmap favicon) {
// TODO Auto-generated method stub
super.onPageStarted(view, url, favicon);
progressBar.setVisibility(View.GONE);
}
public void onPageFinished(WebView view, String url) {
// TODO Auto-generated method stub
super.onPageFinished(view, url);
progressBar.setVisibility(View.GONE);
}