Brendan Fraser Surprises Whisky a Go Go Crowd, Supports Son After Oscars Win

Brendan Fraser's Oscars celebration is now a full-fledged family affair ... after his fun night at a legendary Sunset Strip club where his son hopped onstage to jam out.

TMZ obtained video of Brendan and his son, Leland, having a ball Monday night at Whisky a Go Go in WeHo ... chilling in the green room and signing the performer's wall.

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

Folks who were there tell us Brendan and his son got to the venue around 9 PM and watched an '80s cover band perform ... with Leland even jumping on the stage to play guitar with the band at one point.

Leland's dad was a big hit at the Whisky, as tons of people came up to his table to congratulate him 24 hours after his Academy Award victory ... and we're told he didn't turn away anyone. Folks who met Brendan described him as very down-to-earth.