I have resolved this issue with the help of below solution :-
1.I created an app delegate instance of UIAlertView.
2.I implemented an alert view delegate method "will present alert view...",this method gives me all the alert view objects as a parameter where i have assigned it to my app delegate object of alert view.
3.On application life cycle method "applicationDidEnterBackground" i am using below code ...,which resigns my alert dailog on coming from background to foreground...
if ([AppDelegate shared].alertObserver) {
//Dismissing alert which was shown before moving to background
[[AppDelegate shared].alertObserver dismissWithClickedButtonIndex:0 animated:NO];
[AppDelegate shared].alertObserver=nil;
}