A member of the public contacted police after the comedian spoke about God during an interview with RTE in February 2015, the Irish Independent reported.
The individual, who wished to remain anonymous, told the news outlet it was their “civic duty” to report the comments which he alleges were in breach of the Defamation Act.
He said he had recently been contacted by police after following up the complaint with them late last year.
A spokeswoman for the Garda said: “We are not commenting on an ongoing investigation.”
The footage, which showed Stephen quizzed by TV presenter Gay Byrne, went viral after it was aired and has now been seen more than seven million times on YouTube.
Asked what he would say if he was confronted by God, Stephen replied: “How dare you create a world in which there is such misery that is not our fault? It’s not right.
“It’s utterly, utterly evil.
“Why should I respect a capricious, mean-minded, stupid God who creates a world which is so full of injustice and pain?”
Questioned on how he would react if he was locked outside the pearly gates, he responded: “I would say, ‘Bone cancer in children? What’s that about?’
“Because the God who created this universe, if it was created by God, is quite clearly a maniac, utter maniac.
“Totally selfish. We have to spend our life on our knees thanking him? What kind of God would do that?”
The offence of blasphemy, included in the Defamation Act, is punishable by a fine of 25,000 euro (£21,000) under Irish law.