Eren attacked Mikasa in season one of Attack On Titan when he lost control of his body and actions after transforming into his titan, however, no clear reason has been provided for the attack.
Eren attacking Mikasa in season one of Attack On Titan appeared to be out of character for him, as it was a result of him transforming into his titan. The attack was out of character for his titan as well, which is usually focused on eating humans but with no desire to kill them for no reason. Whilst Eren was transforming, it was clear that he intended to kill Mikasa, so much so that he ended up injuring himself.
There has been no real reason provided for why Eren attacked Mikasa, as the storyline attributed it to him finding his way as a titan. Fans, however, believe that the attack was because he did not want Mikasa to be on his team from the onset, and he supposedly used his transformation to express his fury.