Kenya police say they arrested Mohamed Abdi Ali, a medical intern who is accused of radicalising and recruiting university students.
Mohammed Abdi Ali, a medical intern at Wote Hospital with his wife, a medical student in Uganda and two other accomplices Ahmed Hish and Farah Dagane were arrested for plotting a biological attack Kenya.
The medics were also recruiting university students for the Islamic State group ISIS, which is replicating Al-Shabab in the use of Kenyan youths to attack the country.
Activists however said one of those the police said was arrested, Ahmed Hish is a rights campaigner who had gone missing.
They have accused the police of making a false statement after mounting pressure about his whereabouts.
The suspects were said to be planning an attack larger than the one on the Westgate Mall and Garrisa University which killed 67 and 148 people respectively.
At least two dozen Kenyans travelled to Libya to join the ISIS group and fears of attacking Western targets like resorts have heightened.
Kenyan police said the accused were helped by medical experts but fell short of releasing the name of the “experts” to use anthrax to carry out the attack.
Since 2011, Kenyan forces have been aiding Somali troops to fight Al-Shabab militants.