Thousands gathered at the college on Saturday, with about 100 taking part in a run to commemorate the victims.
Later, prayers and candlelight vigils were held in Garissa, in the capital Nairobi and elsewhere, led by government officials.
Four al-Shabab militants shot students in their dormitories before rounding up and killing dozens more.
It was the deadliest attack in Kenya since al-Qaeda's bombing of the US embassy in Nairobi in 1998, which killed 213 people.
Al-Qaeda-linked al-Shabab, which is based in neighbouring Somalia, has carried out a number of attacks against Kenyan targets.
The group says it is retaliating for acts by Kenya's security forces, which are part of the African Union's mission in Somalia against al-Shabab.