JOIN USKarim bin Farhan al-Messeyden al-Atawi was found guilty of stabbing to death brothers Hammud and Saud Ali al-Atawi, the ministry said in a statement carried by SPA state news agency.
In a separate case, Ahmed bin Awdeh al-Atawi was convicted for having shot dead an Afghani, Mohammed Zaki Zaher Khan, with a machine gun, the ministry said in a separate statement.
The executions bring the total number of beheadings in Saudi Arabia this year to at least 48.
Saudi Arabia has "resumed executions at an alarming pace" since the end of August, Amnesty International said last month, adding that around 140 prisoners were believed to be on death row in the ultra-conservative Muslim kingdom.
The London-based watchdog said Saudi Arabia was one of a minority of states that voted against a UN General Assembly resolution last December calling for a worldwide moratorium on executions.
Rape, murder, apostasy, armed robbery and drug trafficking are all punishable by death under the oil-rich Gulf state's strict interpretation of Islamic sharia law.