Yes, if an antibody on the surface of a B-cell binds to the target, then the B-cell will proliferate and attract other immune cells to it to respond to the disease. If it's an antibody that's been secreted, then there are immune cells monitoring the body, looking out for them, and the immune cells will then find them and respond appropriately.

In general (in a healthy individual), the immune is brilliant at knowing when to respond and when not to - T cells and B cells develop in lymph nodes/follicles in your body and go through both negative and positive selection steps - so they bind to foreign substances (ie diseases) but don't respond to your own body (ie they don't attack your own cells).