The surplus is increasing faster than last year, the Bank of Korea (BOK) said.
The BOK has forecast that the yearly surplus will reach $84 billion in 2014, up from $70.73 billion recorded in 2013, which accounted for about 6 percent of the gross domestic product (GDP).
In August alone, the surplus totaled $7.27 billion, down from $7.84 billion in July, the central bank said.