Fresno police officers arrested 22-year-old Mario Osornio late Saturday night at a home on East Platt Avenue near Fourth Street.
Authorities believe a group of family members were gathered at the home and were drinking. They say the altercation started when the suspect was accused of taking the victim's cell phone.
That turned out to be false, but the suspect became upset, took out a knife, and stabbed his cousin.
The victim is expected to be okay. The stabbing is currently under investigation.