According to IGN, Monster Hunter Series producer Tsuyoshi Tanaka stated at a Tokyo event held in commemoration of the completion of Monster Hunter 2, that Capcom hopes to release a new entry in the series for the PSP.
Note that this game is different from Monster Hunter Freedom due out this spring. Freedom is based on Monster Hunter G which originally came out for the PS2. This is a completely new entry in the series that will be made for the PSP. Hopefully we will not have to wait too long after Japan gets it to have it released in North America.