South African Olympic and Paralympic sprinter Oscar Pistorius leaves the North Gauteng High Court in Pretoria, in this September 12, 2014 file photo. [Photo/Agencies]

Steenkamp's family have said they are unhappy with Pistorius's sentence and questioned the verdict in public in August.

Tania Koen, a lawyer for the Steenkamp family which has opposed early parole, told state broadcaster SABC last week: "Nothing is changed in their lives. Reeva is not coming back."

Prosecutors argue the verdict should be one of murder because Pistorius must have known that the person behind the door could be killed. The appeal is due to be heard on Nov. 3.

The state will argue that the trial judge misinterpreted parts of the law and ignored vital evidence. A murder conviction would result in a minimum sentence of 15 years in prison.

A panel of five judges will hear the appeal. They could either reject the prosecution's appeal, order a retrial or convict Pistorius of murder themselves, legal experts say.