In a small saucepan, heat the rice syrup and sea salt over low heat until liquefied. Add the peanut butter and cook, stirring, until well combined and heated through but not boiling, about 5 minutes.
Pour the cereal into a large bowl. Using a rubber spatula, stir the peanut butter mixture and carob chips, if using, into the cereal.
Lightly oil a 9-by-13-inch baking dish. Transfer the crispy rice mixture to the baking dish, pressing into an even layer. Let cool for 1 hour before cutting into squares.