The other key sectors of mining, manufacturing and trade also registered growth.
GDP rose 1.1% on an unadjusted year-on-year basis in the second quarter, compared with 1% expansion in the previous three months, the agency said.
Economists polled by Reuters had expected a quarter-on-quarter GDP expansion of 2.1% and a year-on-year expansion of 0.4%.
"The growth rate is not what planners would have wanted. Although it's not negative, it is not at the level that was planned for," said statistician-general Pali Lehohla.
Since emerging from the 2009 recession, South African growth has fallen short of the government's 5% target that economists say is needed to curb unemployment.
"The Q2 GDP data demonstrates some momentum in the economy, but this is unlikely to be sufficient to discourage the Reserve Bank from further easing in support of the economic recovery," said Standard Chartered Bank's chief Africa economist, Razia Khan.