The 34-year-old was released by the Rs at the end of last season after he suffered a knee injury but after working his way back to full fitness in the close season signed a short-term deal in October which has been extended on a monthly basis ever since.
Former Wolves, Hereford, Brentford and Watford man Mahon, has made 457 career appearances but has yet to feature for the Loftus Road side this season and is currently sidelined with a minor hamstring injury.
QPR boss Neil Warnock told the club`s official website: "Gavin is a good pro and I`m pleased we`ve managed to extend his contract by a further month.
"He`s an important member of the squad, who I believe has been instrumental in (regular holding midfielder) Shaun Derry having such a good season, with the knowledge that Gavin is waiting in the wings."
Source: PA
Source: PA