The Twitter account of co-founder and CEO Jack Dorsey was briefly suspended Tuesday night before being reinstated.

It is unclear why Mr. Dorsey’s account was suspended for about a half hour. When his account was reinstated around 9:15 p.m. EST, it initially had fewer than 200 followers. Eventually, his 3.8 million followers were restored.

Mr. Dorsey later tweeted the suspension was an “internal mistake” without detailing further. He also joked, “just setting up my twttr...again,” referring to the first tweet ever sent, by him, 10 years ago.

Users can deactivate their accounts on Twitter, but only the company can suspend them. Twitter suspends accounts when users flag them and the company deems them to be sending spam or abusive tweets. The company also suspends accounts that it detects have been hacked or compromised.

In recent days, Twitter has become more active in suspending accounts that violate its rules. It has also gotten tougher on how its data can be used. On Tuesday, the company published a blog post saying that it was “absolutely unacceptable and prohibited” for developers to track or profile protesters or activists on Twitter.

Social-media accounts of tech executives are a ripe target for hackers. In July, both Mr. Dorsey’s Twitter and Vine accounts were compromised, and Facebook Inc. Chief Executive Mark Zuckerberg’s accounts on both Twitter and Pinterest were hacked in June.