The convention is currently drafting the country's constitution as part of what the military government says is a seven-point roadmap to restoring democracy in Myanmar.
Critics have dismissed the process as a sham.
"People are facing a lot of difficulties and they want to do something, but they are afraid of being beaten to death or arrested"
Ko Bo Kyi, Assistance Association for Political Prisoners
Among those arrested are prominent former student leaders including Ming Ko Naing, Ko Ko Gyi, Ko Jimmy, Ko Pyone Cho, Arnt Bwe Kyaw and Ko Mya Aye, all from the 88 Generation Students group.
Members of the 88 Generation Students were at the forefront of the 1988 pro-democracy uprising.
Most were given lengthy prison terms and were reportedly tortured after the protests were suppressed by the military.
On Monday activists and former student leaders led more than 400 people in a silent march through Yangon, Myanmar's biggest city, after the government arbitrarily increased fuel prices by 100 per cent.
Following the price hike, the overall cost of essential goods and services has skyrocketed, and in some cases prices have more than doubled.
Ko Bo Kyi, the joint secretary of the Assistance Association for Political Prisoners based in Thailand, said at least nine of the detained activists were taken from their homes late on Tuesday.
"From what we know, they are being held at the Kyaik Ka San detention center outside Yangon," he told Al Jazeera. "We don't have all their names but I expect more to be arrested."
|In some cases the price of food has more than|
doubled, protesters say [EPA]
He said some activists have gone into hiding but the rest will continue their activities, including trying to organise a second silent march.
Ko Bo Kyi said security was very tight in Yangon.
"The situation is very bad here. I'm really worried that some activists might be beaten or detained," he said.
"People are facing a lot of difficulties and they want to do something, but they are afraid of being beaten to death or arrested."
He added, "Now people have to use half of their income for bus fares and students are badly affected because many of the universities are located outside of town."
According to US-based activist group, Myanmar authorities had also arrested a number of students.
The US Campaign for Burma, based in Washington, said five university students and three members of another activist group were arrested in separate sweeps.
Reports in government newspapers made no mention of these arrests.
The US group said three members of the Myanmar Development Committee, which had called for a nationwide protest against the fuel price hike, were also arrested along with the five students.
The Myanmar Development Committee has vowed to go ahead with the protests on Wednesday despite the arrests.
Pro-democracy groups in Myanmar have also appealed for support and urgent action from civil society organisations based on the Thai border and the international community.