I do not know what state you are in (it makes a difference), but sometimes items are removed from federal income (so don't appear in the AGI) that the state does not allow to be removed, hence it is added back to the federal AGI as reported on the state.
For example, New Jersey does not permit HSA contributions to be excluded from state income, but the federal law does. So if the Wages of a taxpayer in New Jersey are $40,000 and the employer contributed $1,000 to the employee's HSA, then the real Wages are $41,000. The federal return shows only $40,000.
However, since New Jersey does not allow the exclusion of HSA contributions, the state income (which could be represented as "federal AGI" on the state return) is $41,000.
This is just an example, because I do not know to which state you are referring or to which income item.