The state attorney's office said the head of Maria Elizabeth Macias Castro, 39, was found Saturday near her body with a note whose contents weren't disclosed, CNN reported.
Castro was the editor of the Primera Hora newspaper.
The state office said her death was "attributed to a criminal group," and various media noted there were similarities in her slaying to a double homicide in the area earlier this month.
The bodies of a man and woman, both in their 20s, were found mutilated with signs of torture in the border city of Nuevo Laredo. Both had posted online denunciations of a regional drug cartel, as had Castro, the report said.