It depends. If the refund is taxable at all, it is taxable in 2017. But read on.
If you received a state tax refund in 2017 that was for tax paid in a previous year, then the question of whether or not it is taxable on the federal level depends on whether or not you got a tax benefit for the tax paid in a previous year.
If you did not itemize deductions (i.e., attach Schedule A to your return) in that previous year, then the refund is not taxable in 2017. This will cover the 70% of taxpayers who do not itemize.
If you did itemize in that previous year, then the amount of the refund that is taxable depends on how much that refund helped you itemize in that year, whether some of it pushed you over the standard deduction or all of it did. Immediately after to enter the 1099-G, TurboTax will ask you about itemization in that previous year and figure out for you how much is taxable.
If you are asking if the refund is taxable on the state return, that depends on the state in question and a number of other pieces of data that we don't have yet. Please reply to this post if this is your real question.