I suspect that Avast is blocking popups for Internet Explorer.
If so, how do I turn it off.
No. avast never had this feature…
Maybe Google Toolbar, your browser settings… Tools > Options > Privacy 
avast doesn’t block, it scans content (which it couldn’t do if it blocked) and alerts you to infection. It isn’t a pop-up blocker.
What is your firewall ?
Could it be blocking.