I assume you mean safe in terms of excessive radiation? Even those who paint the most grim picture of the levels of radiation post Fukushima say the problem is not immediate exposure to dangerous levels, but long term exposure to relatively low levels. How high those readings are is open to conjecture. However there is a movement of "citizen geiger counters" who are taking readings across the country all the time. They have identified 20 "hot spots" around Tokyo. I believe one of them is in a ball park in suburban Tokyo, and another is in an area that includes a school. Not exactly tourism heavy locations.
I believe a short stay in Tokyo will not have any lasting effect. about 8 years ago