Or maybe you're not afraid; maybe you're concerned because you believe that's actually going on.
But I'm fairly certain that it's not. In fact, that mosque is probably America's best line of defense against terrorism--and that's one of many reasons that a community should support their local mosques. And why, in general, Americans should support the construction of mosques for American Muslims.
Sadly, the efforts of soldiers fighting and dying overseas (and killing Muslims) foster terrorism by increasing hatred from Muslims and further radicalizing them. I say it's sad because people are dying (on both sides) and the efforts only make the situation worse. American mosques combat the radicalism among Muslims. Visit one--listen to what the preachers are saying. Mosques are open, free, just visit and see what they're teaching. What you'll hear is talk about prayer, fasting, charity, kindness to parents.
If a Muslim has been radicalized, he's probably not going to be too regular at the mosque--he won't hear at the mosque the rhetoric he wants to hear; that is, the kind which validates his radicalism, basically. Instead, he'll be told to be patient, to increase in worship, and act in service to his community. But if he does visit the mosque, then perhaps he'll find a community there who can help to guide him aright.
So don't be afraid of the local mosques. Feel free to visit them--encourage a group visit if you don't want to go alone. Take a group from your church or synagogue--or invite a Muslim you know to come speak at your Sunday school class. Open mutual dialogue at interfaith or multi-faith events--ask them what they are doing, subscribe to their newsletter if they have one. And when you see they're not up to any trouble, consider that the faith of Muslims can positively affect the community in which they live. That it can help take care of the poor, and refugees, the hungry, the homeless, the battered women and orphan children. That it can promote positive activities for youth to keep them "off the streets" and out of trouble. And that it can even help keep the country safer.
Please, visit a mosque.
*By the way, madrasa is just the Arabic word for school.