Various studies have been carried out on chamomile which suggests that it may have health benefits including aiding healing and helping to reduce certain types of anxiety. A study in 2009 seemed to show that the flower had anxiolytic properties (ie it helps to reduce anxiety) but it was only one study so you can't say for sure. Studies also suggest that the effectiveness of chamomile depends on how it is dried and prepared.
However, there is nothing in it that would make you more nervous or awake (eg nothing like the caffeine that you find in coffee or regular tea) and chamomile is harmless to most people (there have been allergic reactions so you never know, but they are rare). In as much as we can be sure of its effects they seem to be good ones, and the mere act of making and drinking a hot, mild drink with no stimulants in it probably has a relaxing effect in itself.