Why is there a small black dot on my screen?

I bought a Macbook Pro 13" with Retina Display (2015) one week ago, and today while browsing in Safari, I noticed a small black dot on the screen. The dot was rendered at that specific place on the website, it is not fixed on my display. Once I zoom in, or refresh the page a few times or even scroll down the page, the dot disappears. I've opened one more blog post on the same website, and I found another identical dot. Once again, it doesn't look that it is fixed in the display, it is more like rendered at that position of the screen.

I've opened few more other websites and pages with white background, I didn't see the dot appear. I'm uploading a picture so you can guys see. Anyone had this problem? I know that it's nothing, but I can't stand it and I need some type of explanation. Thanks for your help. Here's the image: