The children complained of uneasiness after the meals at Katar Middle School, and were admitted at a hospital, a district official said.
"All the children are now safe," he said. "All of them, except two, were discharged after preliminary treatment at the hospital," he added.
Samples of the meal have been collected by police for forensic examination.
According to officials, some children said a lizard was found in the mid-day meal served to them, which claim "may be true or a rumour". However, the doctors who examined the children did not find any sign of poison in their bodies.
Last month, a lizard was found in the mid-day meal served in Sheohar district and a dead rat was found in the mid-day meal served to students of a primary school in Patna.
Last July, 23 children lost their lives after they consumed the mid-day meal cooked in contaminated oil at the government primary school in Dharmasati Gandawan village of Saran district.
The mid-day meal scheme is being run in 72,000 schools across Bihar to serve day meals to 16 million students so that they continue schooling.