Nasser al-Khadri, a candidate in Imran province in northern Yemen, was arrested on Tuesday for tearing up a poster of Ali Abdullah Saleh, the Yemeni president.
Security officials said the head of an election committee representing the opposition also was arrested in Ibb in southern Yemen because he removed Saleh's picture from his car.
Other opposition candidates were arrested in other areas for hanging up posters of presidential contender Faisal bin Shamlan.
Yemen will hold presidential and municipal elections next month.
"Unfortunately, security forces and officials are employing all their powers to help the candidates of the ruling party. They are violating election laws by threatening and intimidating opposition candidates and potential voters," said Ali al-Sarari, the head of bin Shamlan's election campaign.
He said opposition parties have called on the higher election committee to resign after it failed to put a stop to the violations despite repeated complaints.
"This proves that the committee is cooperating with the ruling party," he said.
Bin Shamlan is an oil industry executive who has spoken out against al-Qaeda and won respect for denouncing corruption in Yemen - the ancestral homeland of Osama bin Laden.
Bin Shamlan ran refineries in South Yemen during the 1970s and was an executive for a Saudi oil company in London. He served as minister of infrastructure and minister of oil in the government of South Yemen before the country merged with North Yemen in 1990.
He resigned from parliament in 1995 to protest government corruption.
He was picked by the five main opposition parties to run against Saleh, who provoked criticism in June when he reversed a pledge not to seek another seven-year term. Saleh has been in power for 28 years.
In the run-up to the elections on September 20, at least seven people have been killed, including two soldiers, and 12 injured in election-related violence.