Moments before realizing her close proximity to the giant serpent, the 39-year-old actress can be seen looking serene under a number of lush trees on Friday.
'Hey, Jess, we should get one without your mask in portrait mode,' suggests one of her pals, which prompts her to glance down at the ground.
Before attempting to remove her facial covering, Alba discovers she is merely feet away from the brown and cream reptile, which blended in with the wood chips.
'There's a rattlesnake, right there,' one person says, while another warns, 'Oh crap, it's a rattlesnake, get the hell out of there.'
While the Golden Globe nominee remained relatively calm, behind-the-scenes her friends could be heard shrieking.
'When u unknowingly walk over a 5ft rattle,' she captioned the recording and a close-up shot of the snake.
The alarming post caused quite the stir among her 18.5 million Instagram followers, who flocked to express their relief and shock in the comment section.
'When getting portrait mode saves your life,' January Jones joked, while Orlando Bloom remarked that the snake was, 'a biggie!!!'
Meanwhile Nicole Richie simple commented: 'NOPE.'
Before her photo shoot was cut short, Alba was documenting her chic ensemble, which included a pair of olive green trousers and a blouse with puffed sleeves.
She had her lengthly tresses styled in loose waves and was wearing sandals.
The star opted to keep her nose and mouth covered with a cloth facial covering, which matched her white top.
Amid the coronavirus pandemic, she and her family have been hunkering down at their Los Angeles home, which according to Architectural Digest costs $10 million.
She and her husband, Cash Warren, share 12-year-old Honor, Haven, nine, and two-year-old son Hayes.
The parents of three recently appeared on The Skinny Confidential Him & Her podcast where she discussed how marriage and motherhood have changed her.
Jessica shared that 'I really value the person that I've become in learning how to navigate the world with a partner, with Cash, and then also being a mom to my little people who have taught me, you know, leaps and bounds how to just evolve and try to be more thoughtful, active, conscious person.'
Jessica and Cash spontaneously decided to get married at a Beverly Hills courthouse one day in 2008 while she was heavily pregnant with Honor.