The body parts of the suspected male bomber were found scattered at the Garissa Primary School playing ground near the main dais.
Two pistols, one full and a damaged one were found at the scene too.
Ngatia Iregi, the Northeastern Province deputy criminal investigations chief, said one of the pistols had been stolen from Criminal Investigations Department officers who were victim to an attack by suspected al-Qaeda-linked militants in Garissa last year. One officer died and another was wounded.
Narc Kenya presidential candidate Martha Karua was to hold a rally in the town and was to end up at the damaged scene, one of her aides confirmed.
“We are aware of what happened there and we are trying to see what to do next and if we will go on with our rally there,” said an aide.
Karua has been on a tour of North Eastern and was in Wajir on Saturday.
According to the Garissa County Commissioner Maalim Mohammed, police had initially thought that the explosive material was thrown from a moving vehicle near Locus Hotel.
Kenya has experienced a spate attacks since it sent its troops to Somalia in October 2011 to fight the al-Qaeda-linked Alshabab insurgents who were blamed for attacks on Kenya soil. The militants vowed to carry out attacks in Kenya in retaliation.