There are so many people who claim that they are self-taught graphic designers that actually pursuing a graphic design degree online is a step up. What I mean to say is that it shouldn’t be so hard and all that different from pursuing any other degree. That being said, online classes are not meant for everyone and you should take them only if you have the focus and discipline to follow through.
Coming back to your question, I have taken online classes from Stevens-Henager College, although not in graphic design. But if I am not wrong, they do offer a graphic design degree online as well. You could check out more details on their website.