It appears to be. It is hard to accurately categorize a movement that is still in progress, but to date, virtually all of the major protests and organizing seems to be taking place in major cities. Urban areas in general tend to be more liberal, and more concerned with progressive social causes, as was the Progressive Movement of the late 19th century.
It also makes more sense that OWS be concentrated in the cities as that's where Wall Street is, as well as the other financial institutions and corporations that the movement is against or wants reformed.
To be clear, the Tea Party movement also has some urban support, as the conservatives are usually the minority in the cities, and feel unrepresented, which was motivating for them. But you're right, the base of support tended to be in rural communities and agricultural states which tend to vote Republican. I also think the Tea Party had a strong following in southern states, which had large numbers of people who did not support Obama for President and were looking for an outlet for their frustration.