Daymond Agnew, 34, entered a plea of not guilty Tuesday to the murder charge as well as an enhancement of using a knife.
Agnew will return to Contra Costa Superior Court on Nov. 14 for a preliminary hearing.
Contra Costa Deputy District Attorney Simon O'Connell said their investigation has determined Agnew was causing a disturbance inside the Oliver's Ace Hardware store in El Sobrante at about 9 a.m. on August 4.
O'Connell said hardware store employee Daniel Stone, 51, confronted Agnew and the suspect became angry.
O'Connell said Agnew attacked Stone inside the store, then followed him outside and killed Stone in the parking lot.