The rally is to be held in the capital of Minsk at 7 pm Sunday night (5 pm GMT).
Opposition backers said they, too, were planning rallies to protest alleged vote rigging and demand a rerun.
Exit polls by two groups loyal to Lukashenko projected that the incumbent would get more than 80 percent of the vote. They made their polls public only a few hours after voting began, in defiance of the common practice of not releasing exit polling results until the end of voting.
Belarus' hard-line president routinely harassed opposition leaders and media in the run-up to Sunday's ballot, and has banned election-day rallies in an effort to prevent the kind of protests that had swept opposition leaders into power in Ukraine, Georgia and Kyrgyzstan.
