"I've already said more than once that I'm really enjoying myself at Feyenoord," the 49-year-old Koeman told the club's website (www.feyenoord.nl).
He joined the club on a one-year contract in July 2011 after Mario Been stepped down and added a year to the deal in January.
Koeman, the younger brother of former Feyenoord manager Erwin, began his coaching career at Vitesse Arnhem.
He won three Dutch titles with Ajax Amsterdam and PSV Eindhoven and has also worked for Benfica and Valencia.
Feyenoord are fifth in the Dutch league four points behind leaders Twente Enschede. (Reporting by Theo Ruizenaar; Editing by Mark Pangallo)