I'm unsure exactly of the literacy rates of people within the Roman Era prior to the year 0, but by 50-75 CE, literacy rates were about 10%. A great book on this is [Literacy in the Roman World (Journal of Roman Archaeology Supplementary Series #3)] (http://www.amazon.com/Literacy-Journal-Archaeology-Supplementary-Series/dp/1887829032) This book goes through various areas to give approximations. From my research, classes, and readings, it appears that most scholars estimate that literacy (the ability to read), was, as I said around 10% at this time, but that the ability to write was significantly lower, perhaps half of that number. That said, some areas had much higher literacy rates than others.

Here is also an excerpt from noted New Testament Scholar Bart Ehrman's book Jesus, Interrupted: Revealing the Hidden Contradictions in the Bible (And Why We Don't Know About Them) which also backs the rather vague estimate of it being around 10%:

How many could read? Illiteracy was widespread throughout the Roman Empire. At the best of times maybe 10 percent of the population was roughly literate. And that 10 percent would be the leisured classes— upper-class people who had the time and money to get an education (and their slaves and servants taught to read for the benefit of such services to their masters). Everyone else worked from an early age and was unable to afford the time or expense of an education.

Let me know if you have any other follow up questions