The virus is carried by mosquitos.
About 170 horses have been diagnosed with the disease, up from 25 last year. The increased infection among horses is worrisome because the disease is potentially fatal to humans.
Two young children have been diagnosed with Eastern equine encephalitis in Florida so far this year.
Health officials say there are usually two to five cases in Florida each year.
The reason for the sharp increase in horse cases may be a combination of an increase in mosquitos brought by heavy rains and some horse owners not realizing they need to vaccinate their animals twice a year.
The state has about a half million horses.