This appears to be a GOOGLE FONT which means it is Open Source. Here is what GOOGLE has to say about the usage of their open source fonts...
Open Source Fonts
All of the fonts are Open Source. This means that you are free to share your favorites with friends and colleagues. You can even customize them for your own use, or collaborate with the original designer to improve them. And you can use them in every way you want, privately or commercially — in print, on your computer, or in your websites.
We are working with designers around the world to publish quality typeface designs that are made for the web. If you are a type designer and would like to discuss this, please get in touch.
Many of Google's own web pages are already using Google Fonts, such as Google's About page and Google's World Wonders Project which use Open Sans.
— The Google Fonts Team