Carp, who bounced between Triple-A Tacoma and the Mariners for the previous two seasons, grabbed hold of his first full-time opportunity with Seattle by hitting .313 with 25 RBIs, eight doubles and six home runs in 27 games in August.
"It's a great accomplishment," Carp said. "Just to play a month was great, and to have the success I had was a lot of fun. We've got one more month now and I'd like to have another good one."
The 25-year-old posted a .545 slugging percentage and a .353 on-base percentage in August and tied a Mariners rookie record with 25 RBIs in a single month, set by Danny Tartabull in July 1986.
Carp filled in for injured first baseman Justin Smoak for most of August at first base. He's now playing left field and designated hitter, two spots that likely will be his future with the Mariners, according to manager Eric Wedge.
Carp had a 20-game hitting streak snapped on Aug. 21 after batting .363 during that surge.
"It's been a crazy year, up and down, up and down," Carp said. "To finally have a good 'up' means a lot. We went through some struggles as a team, but the rookies have had a lot of success and it means a lot just to be able to play that much."
Carp is the fourth Mariners player to receive AL Rookie of the Month honors and the first position player since Ichiro Suzuki did it four times in 2001. Pitcher Michael Pineda earned the honor this April.