The incident happened at a shop in Eltham High Street just before 3.20pm on January 25.
Officers attended and found that a 25-year-old man had allegedly attacked a shop worker and a dog, believed to be an XL Bully, reportedly bit two men.
The man was tasered as he tried to leave and he was arrested on suspicion of actual bodily harm and being in possession of a dog which was dangerously out of control.
He remains in custody for questioning.
The injuries of the two men, who were bitten, are not life-changing or life-threatening.
Cordons and road closures which were put in place for safety were removed shortly after.
Police enquiries are ongoing.
A spokesperson for Metropolitan Police said: “Police were called at 3.18pm on Saturday, 25 January to reports of a dog attack in Eltham.
“Officers attended the scene at Eltham High Street, SE9, where a 25-year-old man had allegedly attacked a shop worker and a dog, believed to be an XL Bully, had allegedly bitten two men also present.
“The man was Tasered when he tried to leave and subsequently arrested on suspicion for actual bodily harm and being in possession of a dog which was dangerously out of control.
“He remains in custody for questioning.
“The injuries of the two adults who were bitten are not life-changing or life-threatening.
“Cordons and road closures which were put in place for safety were removed shortly afterwards.
“Enquiries are ongoing.”