This most frequently happens for two reasons:
1. Convertible Note Interest
Under U.S. tax law, the interest that accrues on convertible notes during a period usually must be included in taxable income even when the company does not have an obligation to pay it during the period.
2. Passthrough Income from LLC's & Partnerships
If a fund you invested in invested in a passthrough operating portfolio company, that operating company may pass through taxable income without a corresponding cash distribution. This allocation may in turn flow through to your K-1.