The family has confirmed the death of Mattera who was known for his poetry and his criticism of the anti-apartheid government and said they will issue a full statement in due course.
He recently received the Artfluence Human Rights Award 2022 for his commitment to human rights and community development.
On Saturday, the city of Joburg paid tribute to the 86-year-old poet as part of the 60th birthday celebrations.
Mattera was born in 1935. Many have described Mattera as a voice of compassion and an activist who cared deeply about his community.
He grew up in Sophiatown before the apartheid government moved his family to Westbury.
During the campaign against the Sophiatown evictions, Mattera became a political activist and member of the African National Congress.