From the U.S. State Department:

The U.S. Department of State alerts U.S. citizens to the potential for unrest in Bahrain. This Travel Alert supersedes the Travel Alert dated January 23, 2012, and expires on June 30, 2012. It updates information about spontaneous and at times violent demonstrations.

All travelers to Bahrain face increased scrutiny from Bahraini authorities, and the Government of Bahrain has refused to allow some U.S. citizens permission to enter Bahrain. The airport remains open and operational.

Spontaneous and at times violent anti-government demonstrations occur in some neighborhoods, particularly at night and on weekends. These demonstrations have included blockades of major highways with burning debris and establishment of unofficial checkpoints. Participants have thrown rocks and Molotov cocktails and used various other homemade weapons to include isolated use of crude improvised explosive devices. The Ministry of Interior maintains official checkpoints in some areas and routinely uses tear gas and stun grenades along with birdshot and other crowd control measures against demonstrators. Violent clashes between security forces and demonstrators can make travel in and around Bahrain dangerous without advance warning. ...

U.S. State Department Alert