Governor Lou Leon Guerrero said out of 38 samples, two tested positive for the virus, and one other case was reported earlier from Naval Hospital.
Five people have died from the virus in the US territory.
Meanwhile, roadblocks across Guam will be lifted today.
Ms Leon Guerrero said the situation will be closely monitored after the roadblocks are lifted, and a test programme will be expanded.
Many restrictions on everyday life will remain.