The news comes less than two weeks after the world's richest man completed his $44bn takeover of Twitter.
Tesla's share price has fallen by more than 50% since the start of this year.
Separately, Tesla is recalling just over 40,000 of its vehicles in the US because of a potential problem with their power-steering.
The reason for the latest sales, which took place in the last week, has not yet been disclosed.
The latest sale brings the total value of Tesla shares sold by Mr Musk to almost $20bn since he announced earlier this year that he had bought a stake in Twitter.
He sold $8.5bn of Tesla stock in April this year and around another $7bn worth in August.
Also in August, Tesla shareholders approved a three-for-one stock split, which is behind part of the fall in the value of the shares.Electric car recalls
On Tuesday Tesla recalled just over 40,000 of its cars in the US because of a potential power-steering problem.
The electric car manufacturer said the vehicles' power-steering assist system may fail on rough roads or after hitting a pothole.
The National Highway Traffic Safety Administration said it could require greater steering effort, especially at low speeds, increasing crash risks.
Tesla has released a software update to recalibrate the system.
It was unaware of any injuries or deaths in connection with the problem, it said.
Since taking control of Twitter last month Mr Musk has cut around 50% of the company's workforce.
Mr Musk tweeted that he had "no choice" but to slash the company's workforce as the firm is losing more than $4m a day.
He has also blamed "activist groups pressuring advertisers" for a "massive drop in revenue".
The shake-up of the social media platform includes charging users $8 for blue check verification marks.