"Unplugged" is a mix of Keys originals and covers with guests including Common, Mos Def, Damian Marley and Maroon 5's Adam Levine.
Nickelback's "All the Right Reasons" dropped to No. 2, while Gary Allan's "Tough All Over" clocked in a career-best at No. 3 on the Billboard 200 and No. 1 on the Top Country Albums chart.
Black Eyed Peas' "Monkey Business" rebounded to No. 4 and Kanye West's "Late Registration" moved up a notch to No. 5.
Ricky Martin's first English album in five years, "Life," hit the albums chart at No. 6, followed by Sheryl Crow's "Wildflower," Twista's "The Day After," Gretchen Wilson's "All Jacked Up" and Young Jeezy's "Let's Get It: Thug Motivation."
Overall, U.S. album sales were down 6 percent from last week at 10 million units -- about 2.6 percent behind the same week last year, Billboard reported. Year-to-date sales trail 2004 by 10 percent at 436 million units.