False. But you knew that, didn't you?
Well, not so fast. Let's think about this a minute. To be "Iranian" could mean to be a citizen of Iran. Using that definition, there must be lots of Iranians who are also Arabs. "Iranian" in this sense refers to a person's citizenship in a particular state.
Or "Iranian" could refer to someone who grew up speaking Farsi and thinking of herself as Persian, regardless of her citizenship. "Iranian" in this case refers to a people or a culture, not a state.
Speaking of Arabs, here's an interesting collection of impressions of Arabs and Arab culture, by a Westerner. I'm not saying it's a wonderful, loving tribute, just that it's interesting.
For extra credit, answer this question: what's the most populous Islamic country? Hint: it's not an Arab country.
And, hey, while we're at it, why do Iranians call themselves "Persians"? And what language do they speak? Read all about it here (bonus: there's a Nazi connection!).