State officials said the new sample is from the same small Miami Beach neighborhood where three other samples tested positive for Zika on Sept. 1.
"This new discovery shows that the Zika threat continues to grow," Miami Beach mayor Philip Levine said in a statement.
But in a statement, the Department of Agriculture and Consumer Services reminded concerned residents that the state "has tested more than 2,900 mosquito samples, consisting of nearly 48,000 mosquitoes, since May, and these four total samples from a small area in Miami Beach are the only samples to test positive."
Florida's commissioner of agriculture, Adam H. Putnam, said, "This find underscores the continued need already underway in Miami-Dade to employ an aggressive and comprehensive mosquito control strategy. Only with a multi-faceted approach to controlling the Zika-carrying mosquito will we be able to protect Floridians and visitors."
And Miami-Dade County mayor Carlos A. Gimenez added, "The fact that we have identified a fourth Zika-positive mosquito pool in Miami Beach serves as further confirmation that we must continue our proactive and aggressive approach to controlling the mosquito population, including our recent decision to begin aerial spraying in combination with larvicide treatment by truck."
The next round is scheduled for 6 a.m. Sunday.