If the taxable amount of your social security benefits increased from last year, it means that your income from other sources went up.  The amount of social security that can be taxed ranges from 0%-85%, depending on how much additional income you have.

Here's a link to IRS Publication 915 which discusses how the taxable portion is calculated (see page 2, "Are any of your benefits taxable?"):  https://www.irs.gov/pub/irs-pdf/p915.pdf.