The striker aimed an elbow at Brentford's Yehor Yarmoliuk midway through the second-half, but fortunately missed.
The incident occured in front of ref Andy Madley, who failed to act.
Frank said afterwards: "I've seen it. I think it's a red card. You can't swing your arm like that. It's like if you want to swing your arm - hit or no hit - it's a red card.
"My obligations to you guys mean I haven't been able to speak to the referee yet. I'll have a good conversation. I understand it's not easy to get everything right."
Meanwhile, Brighton boss Fabian Hurzeler insisted: "For me, it’s not a red card. He (Pedro) tried to get free from a personal duel."
Ex-ref Mark Clattenburg also said: "If we look at the laws of the game as it's written, it has to be to strike an opponent or attempt to strike an opponent.
"Because there was no contact he can't be sent off the field of play for the contact. Therefore, it's whether he attempted to strike the opponent. The more I look at it, because it's an unusual action, especially from behind he is looking towards Andy Madley when he swings his arm. He keeps his arm quite close to his body and I think it's more of a gesture to the referee.
"Andy Madley is in a very good position.
"He couldn't have been sent off for the contact but he could have been sent off for the attempted contact. I believe it's a gesture more than an attempted strike.
"I think Joao Pedro makes a gesture to the referee but if he wanted to swing and use brutality he would have swung his arm out and created contact."