Soon after consuming the meal at the Bhavnath Middle School in Jhanjharpur, they complained of uneasiness followed by burning sensation in their mouth and throat, district official Jagdish Kumar said.
All the children were admitted to a hospital in Jhanjharpur, about 180 km from Patna, he said.
Some children told officials that a dead lizard was found in the meal served to a student. Police collected the samples for forensic test.
But doctors who examined the children did not find any sign of poison in their bodies.
Last week, about 50 children fell ill in Patna district after having mid-day meal in a government school.
In 2013, 23 students died after eating the mid-day meal at a primary school in Saran district.
In Bihar, 16 million students get food under the mid-day meal scheme daily in 72,000 schools.