The fourth quarter of 2018 was the first time in more than two years that Zuckerberg didn't sell a single share of his social media company.
In September 2017 Zuckerberg announced that he would sell 35 million to 75 million shares of Facebook over the next 18 months as part of his promise to give away most of his fortune during his lifetime.
Since then, Zuckerberg has sold about 30.4 million shares worth $5.6 billion, according to Bloomberg.
"It's one of a couple of signs that the company thinks that shares are undervalued," Deutsche Bank analyst Lloyd Walmsley told TheStreet. "The other sign is the recent refresh of the company's share buyback program."
Walmsley, who has a $195 price target and "buy" rating on Facebook, believes that Zuckerberg is waiting for shares to appreciate again before selling them.
Laura Martin of Needham agrees, saying that the pause in selling is "a good sign - he (Zuckerberg) thinks it's too low."
Zuckerberg's fortune has dwindled significantly even without the CEO giving his money away. Since his fortune is tied up in his Facebook stock holdings, the company's 26% decline over the past 12 months has shaved $32.7 billion from his net worth, according to the Bloomberg Billionaires Index.
Don't weep for Zuckerberg just yet, however: His fortune sits at $53.8 billion, making him the world's seventh richest person, according to Bloomberg.
Facebook shares were down 1.7% Thursday as the stock market sold off broadly.