No. Olaf wasn't sentient before Elsa's 'magical accident' in the film, at least according to the Disney authorised tie-in book Anna & Elsa: Sisterhood is the Strongest Magic: Memory and Magic.
As evening fell, the girls stopped skating. It was time to build a special snowman for Anna’s birthday. Elsa swirled her fingers through the air. She created a mound of her famous snowman snow.
Together, Anna and Elsa rolled the snow into three giant snowballs. Elsa stacked them on top of each other. Anna was excited. She wanted to stick on the button eyes and carrot nose, but she was too short. Elsa created a small set of ice steps for her sister. Anna climbed the steps and made the snowman’s face.
That night, Elsa led a sleepy Anna to bed. She tucked her little sister in and said good night. Anna drifted off to sleep.
The next morning, Anna ran to Elsa’s bedroom and shared her dream. In it, she’d sung and danced with an enchanted snowman. She asked Elsa if she could use her powers to make their snowman dance. Elsa smiled. She told Anna that she couldn’t make a dancing snowman, but they could always pretend. Together, they could imagine anything.