Nelson Moncada, 37, was killed late on Wednesday when he tried to drive around a makeshift roadblock set up on an avenue in the El Paraiso district of western Caracas, prosecutors said.
Gunmen "shot him and robbed him of his belongings," they said in a statement.
His death was not for the moment added to a toll kept by prosecutors of fatalities in violent street protests and a crackdown by authorities since April 1. That tally currently stands at 60 deaths.
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However, public ombudsman Tarek William Saab did add the death to a list he is keeping for the same period, which now stands at 65.
Saab called for better investigation of deaths at the roadblocks that have sprung up to filter and extort motorists.
Moncada sat on a bench of judges who in August ratified a 14-year prison sentence given to opposition leader Leopoldo Lopez, who has become a rallying figure for anti-government protesters.
Interior Minister Nestor Reverol intimated the opposition - which the government accuses of being a rightwing group backed by the US - could have been behind the judge's murder because of Lopez's incarceration.
"We are not discarding the possibility that this might be a contract assassination, by hitmen hired by the terrorist right to continue creating and sowing terror," he said.
But Lopez's lawyer, Juan Carlos Gutierrez, told AFP he rejected that hypothesis.
Residents in Caracas have complained that the makeshift roadblocks have become a dangerous criminal phenomenon in which drivers have been attacked by rocks.
