"What that tells you is that from our perspective the risk reward equation works in the United States," he said at the SALT conference in Abu Dhabi, adding that the bulk of the investments are direct, with a small portion indirectly invested through funds.
He said the remaining part of the portfolio is almost equally split between three regions - the United Arab Emirates, Europe and Asia.
Muhairi said Mubadala has invested $2 billion in China in 15-16 sectors from its $10 billion UAE China fund and could step up investments in the mainland.
"China is the UAE's largest trading partner, it is an important economic relationship for us," he said.
Mubadala would want to participate in some "shape, way or form" in the growth of China, which could become the largest economy in the world, Muhairi said.
Technology is a focus for Mubadala, he added.
Mubadala has invested $15 billion in Softbank's Vision Fund I and recently announced plans to invest $250 million through two funds in technology firms in the Middle East and North Africa.
(Reporting by Saeed Azhar and Stanley Carvalho, editing by Louise Heavens)