Mike Nussbaum -- a longtime character actor -- has died due to old age ... TMZ has confirmed.

His daughter, Karen, tells us her father passed away from natural causes in bed Saturday morning at his Chicago home, with her right by his side. We're told Nussbaum had been in hospice over the past year -- and Karen adds, "It was his time."

MN was one of the oldest living actors still working in the biz in recent years -- having recently performed in some plays of late ... but his on-camera résumé is impressive too.

He'll perhaps best be remembered as Gentle Rosenburg from "Men in Black" or Bob Drimmer in "Fatal Attraction" ... or even the principal from "Field of Dreams." He'd been in a lot.

Some other notable movie credits of his include ... "House of Games," "Things Change," "Desperate Hours," "Losing Isaiah," "Steal Big Steal Little," "Dirty Work," "Osso Bucco," "Towing," "Tom of Your Life" and more. He'd acted in some big TV shows as well through the years.

Just a taste of some of the series he'd been in ... "Frasier," "L.A. Law," "The Commish," "The X-Files," "Early Edition," "Cupid," "The Chicago Code," "The Equalizer," "Spenser: For Hire," etc.

Nussbaum was considered a legend in the local theater scene there in Chi-Town. He was 99, and just a week short of reaching age 100.

RIP