Police took a group of protesters in for questioning on Thursday morning in Pyay town in Bago region, after a demonstration by around 100 residents against power cuts.
The rallies are the first since a deadly crackdown on monk-led protests in 2007, and are being closely watched as a test of the new quasi-civilian government's tolerance of public discontent.
"Three or four NLD members were arrested," said Nyan Win, a spokesman for opposition leader Aung San Suu Kyi's National League for Democracy (NLD) party.
"We have asked the NLD members to obey the party's instruction... not to participate in the protest without permisson from the headquarters," he said.
Local resident Nyi Nyi Aung says protesters, who were demanding 24-hour electricity, were roughly handled by around 50 police.
"About 50 police arrived and asked the people to stop... some people were injured," he said, adding six people were detained and later released.
Rallies started at the weekend in Mandalay, Burma's second-largest city, and have also spread to Rangoon, where about 250 residents on Wednesday defied a police request to disperse as they gathered at the landmark Sule Pagoda.
On Tuesday about 10 NLD members were held by police for several hours in Mandalay for questioning and later released without charge.
The government directly addressed the protests and power shortage issue on Thursday.
"It is usual in a democratic country that people express their desire by protesting. But they need to be lawful," presidential adviser Ko Ko Hlaing told a press briefing.
"They can protest to the extent that the law permits. According to the law, if they want to protest they need to inform the police station and get permission."
Burma suffers crippling power cuts and only 13 per cent of the population has access to electricity, according to 2009 figures from the World Bank.