"North Korea and the leadership of North Korea is only predictable in one sense and that is - if you base it historically - they will continue to provocate," Mullen told reporters after arriving in Beijing.
"The provocations I think now are potentially more dangerous than they have been in the past."
Tensions in Northeast Asia have risen sharply since South Korea accused the North of torpedoing a warship in March 2010, killing 46 sailors.
Pyongyang angrily denied the charge but went on to shell a border island in November, killing four South Koreans including two civilians.
Six-party nuclear disarmament talks, grouping the two Koreas, China, Japan, Russia and the United States, have been stalled since the North abandoned them in April 2009. It staged its second nuclear test a month later.
"All of us are focused on a stable outcome here of what is increasingly a difficult challenge with respect to the leadership in North Korea and what it might do," Mullen said.
"The Chinese leadership, they have a strong relationship with the leadership in Pyongyang and they exercise that routinely ... continuing to do that as they have done in the past is really important."
On a four-day trip to China, Mullen said he would discuss that and other issues in talks with his counterpart Gen. Chen Bingde and while visiting military bases as the two nations seek to bolster their security cooperation.
"The United States is deepening its commitment to this region and the alliances and partnerships that define our presence there," Mullen said in a speech at Beijing's Renmin University.
"We are, and will remain, a Pacific power, just as China is a Pacific power."
To help build trust with China, the U.S. will conduct anti-piracy drills with China in the Gulf of Aden this year, host medical aid exercises and participate in joint disaster relief exercises next year, he said.
"This region and the global challenges that we face together are just too vital and too vast for us to continue to find obstacles to a better understanding of each other," Mullen told reporters.
The trip coincided with a joint naval exercise that began July 9 with the U.S., Japanese and Australian navies in the South China Sea, where recent Chinese assertiveness over territorial claims has raised tensions.
During his trip, the first to China by a U.S. chairman of the joint chiefs since 2007, Mullen said he would also discuss the Taiwan issue, stability in the South China Sea and confidence-building measures between the two nations.
"Containing China is not the case ... we would like to see China in the long run to be a strong partner with the United States to resolve some of the issues that we have got both regionally and globally," Mullen said.
As tensions in the South China Sea mount, China-U.S. military exchanges have also picked up, with the former US Defense Secretary Robert Gates meeting Chinese Defense Minister Liang Guanglie in Singapore in June.
Gates also visited Beijing in January.
Gates warned last month that clashes could erupt in the South China Sea unless nations adopt a mechanism to settle their territorial disputes peacefully.
Mullen dismissed suggestions that wars in Afghanistan, Iraq and Libya had left the U.S. military unable to play a strong role in the Pacific, describing the idea of America in decline as "just dead wrong."