Harden, who had his second MVP runner-up finish last season, is widely considered the favorite this season. He leads the NBA in scoring (30.6 PPG) and ranks third in assists (8.7 APG) for the Rockets, who have clinched the top seed in the playoffs.
"I'm not sure," Westbrook said when asked if it was Harden's turn to win MVP. "Obviously he's having a good year, a great year. Their team has the best record in the NBA. I'm not sure."
Westbrook's Oklahoma City Thunder beat the Rockets on the road Saturday night 108-102. Westbrook had 24 points, 10 assists, seven rebounds and four steals; Harden collected 26 points, nine assists and four boards.
Before the game, Westbrook acknowledged that Harden is the leading candidate for MVP but said he doesn't have a choice for his successor.
"Nah, I don't have a pick," Westbrook said. "There's a lot of guys doing a lot of great things in the league. Honestly, I don't know kind of what you go off of, because MVP's kind of been picked differently every year. So it depends what criteria, what it is that you guys vote for. But obviously he's leading the charge at the moment."
Cleveland's LeBron James, a four-time MVP, is considered the primary challenger to Harden. James is averaging 27.7 points, 8.7 rebounds and 9.2 assists per game and has been especially dominant since the All-Star break.
Westbrook, whose campaign last season was fueled by becoming the only player in NBA history other than Oscar Robertson to average a triple-double, has not generated much MVP buzz despite posting impressive numbers again this season. He entered Saturday averaging 25.6 points, 9.9 rebounds and a league-leading 10.1 assists per game, but the Thunder have been perceived as disappointing after their offseason trades for Paul George and Carmelo Anthony.