Lyubou Kavalyova told RFE/RL that she has asked Lukashenka to delay the execution until after her son receives a respone to his appeal to the United Nations over the death sentence.
Lukashenka on March 14 rejected a formal appeal made by the two convicts against their execution.
Kavalyova's son, Ulad Kavalyou, and Dzmitry Kanavalau were found guilty in April 2011 of setting off a bomb in an underground station in Minsk. They were sentenced to death in November.
Germany has also appealed to Belarus not to execute the two men. The German Foreign Ministry has summoned the Belarusian ambassador to hear Germany's concerns.
German Chancellor Angela Merkel's spokesman, Steffen Seibert, told journalists on March 16 that Lukashenka's rejection of the execution appeal by the two men on March 14 filled Berlin with "great concern" that the sentences would imminently be carried out.
Seibert added there were "quite considerable doubts and questions" regarding the case against the two men.
The spokesman told reporters that "carrying out the death penalty in these two cases would further strain relations between Germany and Belarus."
Fifteen people died and more than 2,000 were injured in the attack.