The Cambridge, Massachusetts-based company said in a Form 8-K that its board had authorized the buyback program, which doesn't have an expiration date.
The latest buyback program is in addition to the $5 billion previously announced in March.
Earlier this month, Biogen's shares got a boost after the company presented new data on its experimental Alzheimer’s drug aducanumab that didn't reveal any new safety concerns.
In March, Biogen had elected to shelve aducanumab, saying that trial results had suggested the drug was unlikely to work. The company's stock tumbled about 25% following that announcement.
The company reversed the decision in October, saying new data had come to light suggesting that aducanumab could be effective. Additional data showed that infusion, if given for long enough and at high doses, could offer some benefit, the company said.
"Patients who received aducanumab experienced significant benefits on measures of cognition and function such as memory, orientation, and language," the company said in a release, adding that patients also experienced benefits in daily living such as shopping and doing personal finances.
Also In October, Biogen reported third-quarter revenue of $3.6 billion, up 5% from a year ago and beating Wall Street's expectations of $3.5 billion.
The company posted earnings of $1.5 billion, or $8.39 a share, beating forecasts of $8.28 a share. In the same period a year ago, Biogen posted earnings of $7.40 a share on sales of $3.4 billion and net income of $866.6 million.