Mason, 37, was pronounced dead at 6:49 p.m. local time at Holman Correctional Institute in Atmore, The Huntsville Times reported.
His execution for the 1994 execution-style slaying of Huntsville convenience store clerk Angela Cagle came a day after Alabama Gov. Robert Bentley declined to commute his sentence to life in prison without the chance of parole. Defense attorneys' last-ditch appeals to the state's highest court and U.S. Supreme Court were rejected.
Mason used his last statement to apologize to Cagle's family, the executive director of Project Hope to Abolish the Death Penalty said.
The newspaper said the death row inmate was visited at the prison by several people during the day. Prison officials said he didn't eat breakfast and was expected to skip dinner as well, the Times said.
Alabama has put five people to death this year.