Dozens, maybe hundreds. These are mainly european citizens with close personal ties to Iran, not tourists though.Or know something whether there have actually been arrests of european citicens?
As a tourist, the risk is much lower, but not zero. A well-known case is Louis Arnaud https://www.bbc.com/news/world-middle-east-67360438 (and he is not the only one).
I still agree with bwv812 that your risk of ending up in a car accident is higher than getting locked up. Up to you in the end.