Brendan FraserThe Oscars celebration is now a family affair in its own right…after his fun night at a legendary Sunset Strip club where his son took the stage to jam.

TMZ obtained a video of Brendan and his son, Lelandhave a blast Monday night at Whiskey a Go Go in WeHo… chill in the Green Room and sign the Performer’s Wall.

Brendan takes a few beats to find the perfect space to leave his John Hancock, with onlookers making a joke about his handwriting…then Leland follows suit and gets heard too.

People who were there tell us that Brendan and his son arrived at the venue around 9pm and watched an 80s cover band perform…with Leland even jumping on stage to play guitar with the group at any given time.

Leland’s dad was a big hit at the Whiskey, as tons of people came to his table to congratulate him 24 hours after his Oscar win…and we’re told he didn’t turn anyone away. People who have met Brendan have described him as very down to earth.