Mr Najeeb's mother Fatima Nafees and JNU students were protesting outside the high court and they were detained when they tried to enter its premises, police sources said.
"Nearly 23 students were taken to Barakhamba Road police station and Najeeb's mother was taken to Tilak Marg police station," Deputy Commissioner of Police (New Delhi) BK Singh said in a statement.
"She was at her liberty to go anywhere but she intentionally remained present at police station till the arrival of her advocates," he said.
JNU students also alleged that the police "manhandled" Ms Nafees in the name of detaining her and others.
"Delhi Police officers told Ms Nafees that this was not the only case they were handling and brutally manhandled her while detaining," former JNUSU president Mohit Kumar Pandey alleged.
Mr Najeeb (27), a student of M.Sc Biotechnology, had gone missing from the Mahi-Mandvi hostel of Jawaharlal Nehru University on October 15 last year after a scuffle with some students, allegedly affiliated to the Sangh Parivar student wing Akhil Bharatiya Vidyarthi Parishad, the previous night.
The probe was handed over to the CBI on May 16 this year.
The agency was rebuked by the high court in August, when it had failed to file a fresh progress report in the case.
On September 6, the court again directed the CBI to take steps to trace Mr Najeeb.
Ms Nafees had yesterday called for a protest outside the court if the probe agency did not submit a concrete status report.
A bench of Justices GS Sistani and Chander Shekhar said during arguments today, it was "very unhappy" with the CBI after contradictions appeared in what was orally submitted in the court and what it has indicated in its status report.
The bench further said, "We are saying there is complete lack of interest (by the CBI). There is no result either way. No result even on paper."
During a protest before the CBI headquarters two days ago, Ms Nafees had warned of launching a larger agitation if the CBI failed to submit a concrete report in today's hearing.