Constant pop ups re blocked websites

I'm using Trend Security Software on my Dell PC (Microsoft s/w) essentially to check for viruses.  In the last few weeks I've also been getting Trend pops warning me about a suspicious website that should not be opened.  It's annoying because it happens every minute or two or even more frequently.  I have to close the pop up each time to be able to continue with other work I'm doing on the PC.  I don't recognise the website concerned and I've no idea where it's coming from.  How do I eliminate these pop ups?