Thanks for posting and welcome to the Forums. This is a commonly asked question on the forums. In the future, please be sure to search for existing threads before creating a new one. 
This issue is called FOUT (Flash of Unstyled Text) and you can read more on this here: Quick Tip: Avoid FOUT by Adding a Web Font Preloader 1
You can fix this by adding a bit of custom code to your site — Dave explains this more here: Flash of unstyled text - fallback fonts loads initially then switches to google font - #7 by cyberdave
Alternatively, you can try downloading the Google font, then uploading it to your site as a custom font.
I hope this helps!