Around noon ET on Friday, Chase's technical support confirmed on Twitter that "some customers are experiencing difficulties logging in." By about 6 p.m. ET, it said that most online services except for payments were functioning.
Capital One also said on Twitter that it was experiencing "credit card online access issues."
The company did not provide any more indications of when the issue would be resolved.
Chase and Capital One could not immediately be reached for comment on the nature of the issues. The U.S. Department of Homeland Security and Federal Bureau of Investigation told CNBC they had not seen anything suspicious.
JPMorgan Chase and Capital One shares closed 0.6 and 1.3 percent higher on Friday, respectively.