No, humans have never been to the center of the Earth - nor are we likely to ever get there.
The Earth's inner core is thought to be an iron–nickel alloy ball which just happens to be roughly the same temperature as the surface of the Sun (we're talking 5430°C/9806°F) - so not exactly the kind of conditions humans do very well in.
There are several science-fiction novels and films based around the idea of humans travelling to the center of the Earth, but in reality this is considered impossible.
