Are you filing a Joint return or separate returns? The taxable amount of SSA-1099 depends on all the other income on a Joint return including yours. Maybe it wasn't taxable in the past but is this year.
Check the worksheet to see how and why Turbo Tax is making some of it taxable. To see the Social Security Benefits Calculation Worksheet in Turbo Tax Online version you would have to save your return with all the worksheets to your computer. Or if you are using the Desktop CD/Download Software you can switch to Forms Mode (click Forms in the upper right) and click on SS in the list on the left side.
And are you looking at the actual 1040 line 6b? If you are looking at a summary screen or review screen those show the full amount as income and lump a lot of stuff together. You need to check the actual 1040 form and make sure it's right.
See IRS 1040 Instructions Page 28 and the worksheet on 31
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
