It’s an FBI agent. Because the acronym FBI begins with a vowel sound (the F sounds like "eff"), we use the article "an".

It’s an FBI agent. Because the acronym FBI begins with a vowel sound (the F sounds like "eff"), we use the article "an".

My son wants to be an FBI agent.

My son wants to be a FBI agent.

Follow the same strategy with other related phrases and expressions, such as "an FBI investigation", "an FBI informant", "an FBI report", "an FBI file", etc.

The information was acquired in the course of an FBI investigation.

An FBI report was produced and made available to the judge.

Remember, when choosing between "a" and "an", it's the sound, and not the spelling, which is important. For example, we say an F, an FDA inspector, an FYI email, etc.

Did you get an F on your exam?