The 32-year-old referee made the approach to Al Ittihad chief Hamad Al-Senaie, who immediately handed over the WhatsApp messages to SAFF officials who in turn alerted the relevant government authorities, SAFF said.
Al Mirdasi was taken into police custody where he confessed to soliciting the corrupt payment, the statement from the SAFF Ethics Committee added.
Al Ittihad played Al Faisaly in the King's Cup final at Jeddah's King Abdullah Sports City on Saturday, winning in extra-time in a game refereed by former Premier League official Mark Clattenburg.
Clattenburg, who was appointed Head of Refereeing at the SAFF last year, stepped in to replace Al Mirdasi on the eve of the game.
Al Mirdasi has been on the FIFA referees' list since 2011 and officiated at last year's Confederations Cup in Russia.
(Editing by Peter Rutherford)