Mascherano appeared to have an argument with Bennett when the latter cautioned Fernando Torres for dissent, only to get a second caution himself.
"I do not know why I was sent off. I asked the referee what was happening. I did not swear; I was not aggressive and I did not confront him," the Argentine told the Liverpool Echo.
"All I did was ask him what was happening, nothing else, when he (Bennett) showed me the second yellow card and sent me off I could not believe it."
Mascherano's expulsion meant that Rafa Benitez's team had to play more than 45 minutes with a man down against the Premiership leaders.
"I am sorry to my team-mates because that meant we went down to 10 men - and that made things even more difficult for us," he added.
The former West Ham midfielder could get a further ban by the FA for failing to leave the pitch immediately after his sending off.