Mal warning how to eliminate

I recently install avast for Mac free version, now whenever I open safari I get 4-6 warnings Infection Blocked URL:Mal then the url and the process involved. Scan with avast and malware bytes turns up nothing, but the warnings continue. What is the best way to resolve this. Thanks in advance! I have attached screenshot of warnings.

Try clear safari surf history/cache

I did clear the specific reference. It went away for a few days but now is back. Did not visit site again, will clear all this time.
Thanks