The euro shook off the weight of the European Central Bank, holding firm this week even as the ECB cut a key interest rate below zero in a bid to stimulate lending and economic growth.

The euro on Friday traded at roughly the same level against the dollar it was at before the ECB's policy announcement Thursday. Against the dollar, the euro is up 0.1% this week and up 0.4% since hitting a three-month low on May 28.

Behind...