Police sources said the miscreants, riding a motorcycle hurled a grenade at the corner meeting in Mardan district, some 50 kilometres from Peshawar, the provincial capital of Khyber Pakhtunkhwa.
The miscreants fled after the attack.
Tehreek-i-Insaf said nearly 30 people were present at the meeting. No group claimed responsibility.
Also on Sunday, a Tehreek-i-Insaf office in Peshawar was targeted with a timed-device. However, there was no casualty in the incident.
Violence has been on the rise ahead of the May 11 general elections, with the Tehreek-i-Taliban Pakistan targeting the Awami National Party (ANP), the Muttahida Qaumi Movement (MQM) and the Pakistan Peoples Party (PPP) terming them "secular".