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.