The Fed has been buying $85 billion of Bonds a month to help stimulate the economy and housing market. As you may know, home loan rates are tied to the Mortgage Bonds which are a part of this monthly sale. Because of this, the home loan rates have stayed relatively low.
Just how long the Fed will keep buying these bonds is up for discussion and key to this decision will be the economic data in the coming weeks. It is possible that this stimulus could taper off as early as mid-September causing the mortgage rates to increase.