Human Rights in China said Liu Shaokun had been ordered to serve a year of "re-education through labour".
Mr Liu was detained for "disseminating rumours and destroying social order", the group said.
The 12 May quake killed nearly 70,000 people. Many of those who died were children whose schools collapsed.
The poor condition of the school buildings has become a sensitive political issue for the government, and grieving parents have staged numerous protests demanding an inquiry.
Many have accused local officials of colluding with builders to allow them to get away with cheap and unsafe practices.
"Instead of investigating and pursuing accountability for shoddy and dangerous school buildings, the authorities are resorting to re-education through labour to silence and lock up concerned citizens like teacher Liu Shaokun and others," said Human Rights in China Executive Director Sharon Hom.
According to Human Rights in China, Mr Liu's wife was informed by police last week that the teacher, from Guanghan Middle School in Deyang city, had been sent to a labour camp.
The "re-education through labour" system allows police to incarcerate a crime suspect for up to four years without the need for a criminal trial or a formal charge.
The system, in place since 1957, has been widely criticised by the UN and other organisations.