Justin Bieber showed his serious side as he spoke to teenage campaigner Malala Yousafzai.

The Canadian pop star shared a FaceTime photo on Instagram of him chatting to the 17-year-old Pakistani activist, who survived after being shot by the Taliban in October 2012.

"Just got to FaceTime with Malala Yousafzai. She has such an incredible story," he wrote.

"I can't wait to meet her in person and talk about how I can support her and the @malalafund. #love."

Justin followed up the post with a series of motivational quotes on Twitter, such as "Make a positive difference in the world" and "Smile."

But he couldn't resist sharing another selfie of his toned abs and tattooed body soon afterwards.

It comes after his hearing to determine whether the Believe singer will be tried on charges of driving under the influence and resisting arrest was postponed by the Miami-Dade County judge to August 13.

The 20-year-old singer was arrested on January 23 in Miami Beach after what police described as an illegal street race between Justin and a friend.

Alcohol breath tests found Justin's level below the 0.02 limit for underage drivers, but urine tests showed the presence of marijuana and an anti-anxiety drug. He was also charged with driving on an expired licence.