The arrestee was identified as Amir Farhad Adar, 27, son of Amir Soleman of Sadarghat area in the city.
Officer-in-charge of Kotwali Police Station Md Mohsin said police arrested Amir from his residence in Sadarghat area at dawn.
With the arrest of Amir, police managed to arrest all six people accused in the case, the OC added.
The victim Traffic Sergeant Mazharul Alam Sohag of CMP's North Division filed the case, naming six persons and 40 unidentified people, with Kotwali Police Station.
On August 12, a group of youths attacked on-duty traffic police in the city's New Market area after the duty officials sued a biker while he was riding on the wrong side of the road.
The youths also tried to vandalise the police box during the scuffle, said the OC.
The incident happened during the ongoing traffic week across the country, after school and college students launched a countrywide demonstration demanding safe roads.
Gathering in front of New Market traffic box, the accused verbally abused police officials and at one point they started assaulting police, according to the case statement.
They manhandled Constable Mamun, tore apart his uniform and tried to strangle him.
On information, a team of police from Kotwali Police Station rushed there and brought the situation under control.