The officers are conducting thorough searches on vehicles heading to the Jumuia Conference Centre in Limuru, the venue of the outlawed meeting.
Hundreds of heavily armed police officers are patrolling the area to ensure the meeting does not kick off.
Although police have declared the meeting illegal, the former Mungiki leader insists it will go on.
“I have not been formally informed of the cancellation and the meeting will go on as planned,” a defiant Njenga told Capital FM News.
The meeting is meant to counter earlier gatherings held by supporters of Deputy Prime Minister Uhuru Kenyatta and Eldoret North MP William Ruto.
Police cancelled the meeting dubbed Limuru 2B on Monday evening due to security reasons.