Abdullah, whose car was severely damaged by the blast, was uninjured.
According to Interior Ministry spokesman Sediq Sediqqi, at least six people were killed and more than 12 injured at the hotel where the rally was being held. The first explosion was caused by a suicide bomber and the second possibly by a roadside bomb, he said.
No one has yet claimed responsibility for the bombings.
Former Foreign Minister Abdullah is competing against former Finance Minister Ashraf Ghani for the presidency in a runoff scheduled for June 14. Afghanistan's election commission announced that a runoff was necessary because neither candidate secured enough votes to be declared victor. In the primary, Abdullah garnered 45 percento of the vote and Ghani 31.6 percent.