Kim Paik-joon, a key aide of former President Lee Myung-bak, was arrested Wednesday for allegedly receiving more than 400 million won ($375,000) from the National Intelligence Service.
Kim Jin-mo, Lee's presidential secretary for civil affairs from 2009-2011, was arrested on a similar charge.
The arrests are the result of ongoing investigations into the two previous conservative governments, led by Lee and his successor Park Geun-hye, for using NIS funds for personal and other inappropriate purposes.
At the time, Kim worked as senior secretary for administrative affairs to Lee between 2008 and 2012.
Investigators are apparently looking into whether the former president is involved in the illicit use of NIS funds.