If my foreign earned income is below the foreign earned income exclusion threshold amount, am I still required to file a U.S. individual income tax return?

Yes, since the foreign earned income exclusion is voluntary, you must file a tax return to claim the foreign earned income exclusion.  It does not matter if your foreign earnings are below the foreign earned income exclusion threshold.

There are specific requirements that you must satisfy to be eligible to claim the foreign earned income exclusion.