A police official told AFP the individual was stabbed during "scuffles" between the Unity and Assembly Party (PUR), which is led by opposition leader Issa Sall, and pro-government campaigners.
The body was taken to a hospital in Tamboucounda, about 400 kilometres (250 miles) east of Dakar, the source said.
Contacted by AFP, the president's press office confirmed that the person killed was a supporter of the governing Senegalese Democratic Party.
Violence has buffeted Senegal ahead of presidential elections on February 24, despite appeals for calm from religious leaders.
At least two people were "seriously injured" on Sunday in Fatick, a presidential stronghold in Senegal's centre-west, in clashes with supporters of rising opposition candidate Ousmane Sonko, local media reported.
Four people, all Sonko supporters, were badly hurt on February 4 in the northern city of Saint-Louis, Sonko's campaign said.
Senegal, a former French colony, is seen as a beacon of democracy and relative prosperity in West Africa.
But its election campaigns are often tarred by accusations of corruption, influence-peddling and misinformation.