I'm assuming "African American" is being used out of political correctness, and you are not inquiring about how many African expatriates are currently living in America.
The 2000 U.S. census counted a total American population of 281,421,906 citizens.
- 34,658,190 identified as "pure" black
- 36,419,434 identified as being of black/mixed heritage.
The census is due to be completed again next year (2010) so these numbers are likely to be invalid as of then.