He said shoppers who plan to visit one of Minnesota's most popular destinations should be extra vigilant.
Backstory -- Mall of America named as target in al-Shabaab video
"I would say that if anyone is planning to go to the Mall of America today, they've got to be particularly careful," Johnson said. "There will be enhanced security there, but public vigilance, public awareness and public caution in situations like this is particularly important, and it's the environment we're in, frankly."
In the video, a man speaking English and wearing a scarf over his head refers to a 2013 attack on Nairobi's Westgate shopping mall in which gunmen killed 63 shoppers.
"Westgate was just the beginning, and with all hopes of peace forever dashed," the man says. "What if such an attack was to occur in the Mall of America in Minnesota?"
But Johnson says Americans shouldn't let threats like that impact how they live their lives.
"Americans should still feel that they are free to associate, they are free to go to public gatherings, but it's critical that we have public awareness and public participation in our efforts," Johnson said.
Bloomington police statement
Federal, state and local law enforcement partners are aware of the recently released propaganda video that mentions Mall of America, among other malls. At this time, there is no credible threat associated with Mall of America. We will continue to work together at all levels to evaluate this and other information as it becomes available.
We take all security concerns seriously and have responded appropriately. Enhanced security measures to include additional personnel have been implemented and all information is being monitored. We will continue to focus on and to prioritize the safety, security and wellbeing of our citizens and visitors.
Mall of America remains a very safe place and employs an extensive, well-trained professional security force that patrols and monitors activity with a 24-hour presence. Bloomington Police have a permanent presence, with dedicated, full-time staffing at Mall of America. Additionally, several other law enforcement agencies maintain a high visibility in and around the property.
To report suspicious activities, contact your local law enforcement agency at 911. For more information on the Department of Homeland Security's "See Something, Say Something" safety and security initiative, visit http://www.dhs.gov/see-something-say-something.