The United States taxes nonresident aliens on two types of income: First, a nonresident alien who is engaged in a trade or business in the United States is taxed on income that is effectively connected with that trade or business. Second, certain types of U.S.-source payments are subject to income tax withholding.
The determination of when a nonresident alien is engaged in a U.S. trade or business is highly fact-specific and complex. However, keeping assets in a U.S. bank account should not be treated as a U.S. trade or business.
A nonresident alien's interest income is generally subject to U.S. federal income tax withholding at a rate of 30 percent under Section 1441 of the tax code. Interest on bank deposits, however, benefit from an exception under Section 1441(c)(10), so long as that interest is not effectively connected with a U.S. trade or business.
Even though no tax needs to be withheld on interest on a bank deposit, the bank should still report that interest each year to the IRS on Form 1042-S. The IRS can then send that information to the tax authority in Brazil.
Please keep in mind that state and local tax rules are all different, and whether interest on the bank deposits is subject to state or local tax will depend on which state the bank is in.
Also, the United States does tax nonresident aliens on wages paid from a U.S. company, if those wages are treated as U.S.-source income. Generally, wages are U.S.-source income if the employee provides services while physically present in the United States. There are a few exceptions to this rule, but they depend on the amount of wages and other factors that are specific to the employee's situation.
This is an area where you should really consult with a U.S. tax advisor before the employment starts. Maybe your company will pay for it?