That's the on-site analytics widget. Don't worry, only you can see it.

This widget is designed to give you a glimpse of visitor activity while you are on your site. You can see how many people are on your website in total, how many people are on the same page you are, and initiate heatmap reporting (if enabled and available) for the page you are viewing. Clicking on the 'on site' or 'on page' numbers will open another box that shows the list of visitors who are currently on your site and/or on the page you are viewing.