Johnson-Sirleaf also suspended all voting rights associated with the senatorial elections, a statement issued late Wednesday by the Liberian foreign ministry said.
The president has called on the electoral commission responsible for organising the elections to set a new date for the poll along with political parties, independent candidates, the civil society and national and international health institutes.
Johnson-Sirleaf blamed the move on measures and travel restrictions decreed under the state of emergency in order to contain the epidemic.
Holding elections requires a "free, open and transparent" atmosphere which Liberia now lacks, she said.
Liberia is one of the worst-affected countries by the Ebola epidemic that broke out in March in the west African countries and has so far claimed the lives of 3,879 people, mostly in Liberia, Sierra Leone and Guinea.
Ebola spreads through direct contact with blood and bodily fluids of infected persons or animals, causing fever and severe bleeding.