Stephen Lawrence was stabbed to death in 1993
Detectives have not released details of the man's identity but it is understood he is not one of the five suspects previously arrested.
The man was arrested early on Tuesday at his workplace and is being questioned at a police station in Bexleyheath, south east London.
Stephen Lawrence was stabbed to death by a gang of white youths at a bus stop in Eltham in south east London in 1993.
Formal acquittals
Scotland Yard have described the latest move as part of an "ongoing and vibrant" investigation.
In a further development, it has emerged that a building in south east London was searched on Monday by detectives investigating the Lawrence murder.
Ammunition and a quantity of documents were taken away by officers.
A report on the original police investigation found there had been a catalogue of police errors including inadequate searches, botched identity parades and "institutional racism".
Neil Acourt, Gary Dobson and Luke Knight were tried at the Old Bailey but were formally acquitted in April 1996.
The judge ruled that identification evidence from Duwayne Brooks, a friend of Stephen, was inadmissible.
The case against two other men had been discontinued.
Other arrests
But Metropolitan Police Commissioner Sir John Stevens insists he knows who the killers are.
The case led to proposals to end the double jeopardy rule which prevents suspects being tried twice for the same crime.
Under a new system, murder suspects can be retried if a judge rules there is compelling new evidence.