Brendan Dassey, the Wisconsin man whose murder conviction was questioned on the popular “Making a Murderer” documentary series on Netflix, will have to spend at least a little more time in prison.

Brad Schimel, the attorney general in Wisconsin, on Friday appealed a federal judge’s Aug. 12 decision that overturned Mr. Dassey’s conviction in the 2005 killing of Teresa Halbach, a 25-year-old photographer in Manitowoc, Wis. In overturning the conviction, the judge, William E. Duffin of the Eastern District of Wisconsin, gave prosecutors 90 days to schedule a new trial or free him from prison.

The appeal of the judge’s decision means that Mr. Dassey will remain in prison pending the outcome.

The 10-part Netflix series by Laura Ricciardi and Moira Demos, released in December, suggested that police investigators unfairly questioned Mr. Dassey, then 16, without a lawyer or parent present. He was portrayed as mentally unfit, and suggested investigators coerced him into a confession. Judge Duffin agreed, saying that the authorities’ conduct was unconstitutional.