Bites no, disease ye. The bites themselves are no dangerous, save for local reactions or allergic reactions. However ticks can pass disease such as lyme disease.
It depends... ...On the tick. Deer ticks, for example, are often the carriers of the bacteria associated with lyme disease, a chronic and potentially debilitating condition associated with heart, joint and other difficulties. Wood ticks can carry the bacteria that cause rocky mountain spotted fever. Other tick bites are totally harmless and can cause only local irritation. Ultimately it depends on the tick.