Police arrested a 26-year-old man at a warehouse in Alexandria, in Sydney's inner-south, about 2pm (AEST) on Friday.
He was charged with concealing a serious indictable offence and hindering a police investigation.
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The man was refused police bail and was expected to appear in Parramatta Local Court on Saturday.
Mr Keohane had bought a pizza and was walking to his home in Coogee, in Sydney's east, about 3am (AEST) on August 9, 2008, when he was attacked and robbed.
He was hit on the right side of his face with a "sharp object" that was forceful enough to cut through his cheek and lacerate his tongue.
The flooring contractor was bashed in the head about 14 times during the unprovoked attack and was left lying in the street, less than 100m from his doorstep.
Police say Friday's arrest is the fifth to eventuate from their investigation.
Kane Desmond Tupuolamoui, 21, was arrested at a house in Leanyer, Darwin, on July 15, and extradited a day later to face a Sydney court.
He was charged with inflicting grievous bodily harm with intent to murder and aggravated robbery over the attack.
Tupuolamoui's matter was adjourned to Central Local Court on September 2.
Another man, Thomas Isaako, 21, was acquitted in March this year of Mr Keohane's attempted murder, but was sentenced to a 14-year jail term in May for robbery in company and inflicting grievous bodily harm.
Isaako's partner, Chantel Taia, 19, of Matraville, and was handed a suspended jail sentence in November 2008 for failing to tell police about the Keohane's bashing.
Another 39-year-old man was also charged in November 2008 with hindering police and concealing a serious offence over the attack.
