New York-based Committee to Protect Journalists (CPJ) said the government was trying to stifle opposition and media freedom in the country.
They all belonged to the social media activist group Zone 9.
Correspondents say Ethiopia has increasingly faced criticism from donors and human rights groups for jailing its critics - many of whom have sought asylum abroad in fear of being arrested and tortured in jail.
Tom Rhodes CPJ representativeExpressing critical views is not a terrorist act”
"They took training in how to make explosives and planned to train others," the AFP news agency quotes Judge Tareke Alemayehu saying.
The CPJ called on the authorities for the group's immediate release, saying they had been doing their jobs.
"Expressing critical views is not a terrorist act. Once again, the Ethiopian government is misusing anti-terrorism legislation to suppress political dissent and intimidate journalists," Tom Rhodes, CPJ's East Africa representative, said in a statement.