Yes, it is taxable income.
According to the IRS Publication 525, “If you are a U.S. citizen or resident alien, you must report income from sources outside the United States (foreign income) on your tax return unless it is exempt by U.S. law. This is true whether you reside inside or outside the United States and whether or not you receive a Form W2, Wage, and Tax Statement, or Form 1099 from the foreign payer. This applies to earned income (such as wages and tips) as well as unearned income (such as interest, dividends, capital gains, pensions, rents, and royalties).”