According to the BBC, the suggestion came after the girl asked Alexa for a "challenge to do".
"Plug in a phone charger about halfway into a wall outlet, then touch a penny to the exposed prongs," the smart speaker said.
Amazon said it fixed the error as soon as the company became aware of it.
The girl's mother, Kristin Livdahl, described the incident on Twitter.
"We were doing some physical challenges, like laying down and rolling over holding a shoe on your foot, from a (physical education) teacher on YouTube earlier. Bad weather outside. She just wanted another one," she said.
That's when the Echo speaker suggested partaking in the challenge that it had "found on the web," the report said.
The dangerous activity, known as "the penny challenge", began circulating on TikTok and other social media websites about a year ago.
Metals conduct electricity and inserting them into live electrical sockets can cause electric shocks, fires and other damage.
Amazon told the BBC in a statement that it had updated Alexa to prevent the assistant recommending such activity in the future.
"As soon as we became aware of this error, we took swift action to fix it," the company was quoted as saying.