Tensions rose briefly after a bomb-sniffing police dog “alerted” on a scent in the package, which was spotted by a passer-by at Dale Mabry Highway and Santiago Street.
Roads in the area were closed while a bomb team assessed the dog's finding, police said.
Police soon determined the package presented no threat but were investigating to determine what odor caused the dog to react.
The substance that triggered the K-9's alert would have been no threat on its own, police said.
According to police, a woman riding her bike noticed the package under the mailbox. Forty-five minutes later, she saw the package was still there and called 911.
An officer arrived and noticed the package, addressed to the Tampa Bay Times, had no return address or postage.
Dale Mabry Highway was closed to traffic between Bay to Bay Boulevard and San Juan Street for about 90 minutes.