The police removed the body from the scene and launched an investigation, interior ministry spokesperson Waldemar Jose told local media.
The Sinptenu teaching union named the dead man as Lazarino Dos Santos, their national secretary.
He was “shot dead at the door of his house on Monday evening by two police officers on a motorcycle, without justification”, union president Avelino Calunga told AFP.
Angolan security forces have long been criticised for using excessive force.
They have also been accused of killing three people during operations to enforce restrictions brought in to combat the spread of coronavirus two months ago.