"Herlind Kasner, the mother of the chancellor, has died," the spokesman said, without providing further details.
The former Latin and English teacher likely died earlier this month at the age of 90, according to the Bild newspaper and SuperIllu magazine.
She gave birth to the future world leader in Hamburg in 1954, moving to the former East Germany just weeks later with her daughter and husband, Horst Kasner, a pastor who died in 2011.
Merkel answered questions in parliament on Wednesday before heading for a European Union summit on Brexit in Brussels.