A neighbour of murder-accused Oscar Pistorius was questioned in the High Court in Pretoria on Monday after interpreting a call from the athlete, shortly after his girlfriend Reeva Steenkamp was shot dead, as a mistake.

"When he phoned me he said I made a mistake," Johan Stander said under cross-examination from prosecutor Gerrie Nel.

Nel replied: "No he never said that. Why did you want to include that he made a mistake?"

"It was a mistake that I made," Stander replied, playing with his water bottle.

"Why would you make such a mistake? Do you want to assist Mr Pistorius with his defence?" Nel continued.

Stander replied: "My lady I am here to give the truth. In my mind that was a mistake. He never said it was a mistake. That was my understanding."

Stander explained that he interpreted the phone call he received from Pistorius on Valentine's Day last year as a mistake. He said as far as he understood Pistorius did not want to shoot an intruder.

The paralympian called Stander at 3.18am on Valentine's Day last year, shortly after Steenkamp was shot. The Standers and Pistorius both lived in the Silver Woods Estate, Pretoria.

Earlier Stander told the court that when Pistorius called him he said: "Oom (uncle) Johan please, please, please come to my house. I shot Reeva, I thought she was an intruder.

"Please, please, please come quick."

During cross-examination, Nel asked Stander what he thought the mistake was.

"The fact that he shot her? Mr Stander, how can you out of that call say the fact that he shot her was a mistake? Why do you now want to tell the court that he made a mistake by shooting?"

Stander replied: "I'm looking at that telephone call. I can interpret it by saying he made a mistake. He said he thought she was an intruder."

Pistorius is charged with murdering Steenkamp. He shot her through the locked toilet door of his home on February 14 last year, apparently thinking she was an intruder.

Pistorius has pleaded not guilty. The State argues he shot her during an argument.

Stander first met Pistorius in May 2009 when he moved into the estate with his family.

He said the athlete often asked him to look after his house and pets when he went to compete overseas. Stander met Steenkamp in December 2012 and saw her again in January 2013.

The court heard that according to the rules of the estate no additional burglar bars could be installed.

He said he never socialised with Pistorius and he never saw the athlete armed.

"I never visited him in a social capacity," he said.

Since the shooting, he never discussed what happened that night with Pistorius. He said he attended a memorial for Steenkamp that Pistorius had at his house.

Steenkamp's mother June, her lawyer, a friend, Pistorius's uncle Arnold and brother Carl were in court.

Pistorius is also charged with three contraventions of the Firearms Control Act -- one of illegal possession of ammunition and two of discharging a firearm in public.

He allegedly fired a shot from a Glock pistol under a table at a Johannesburg restaurant in January 2013. On September 30, 2012 he allegedly shot through the open sunroof of a car with his 9mm pistol while driving with friends in Modderfontein.

He has also denied guilt on these charges.