BSc student Rahul Yadav of local Bipin Bihari College beat up his teacher when he objected to copying in examination on March 17, police said.
A case was registered against Rahul, who is also the president of the students' union, and some of his friends who were involved in assaulting the teacher, Principal of the College Dr M M Pandey said.
SP (City) Rajesh Kumar Rai said Rahul has been arrested and efforts were on apprehend the remaining accused.
Vaishali district of Bihar had been in the news recently due to mass scale use of unfair means in matriculation examination in which students and their parents and friends were involved.
Since, mass copying was reported from some other districts of Bihar also.